From a stop, in drive or od, I let off the brake, and the car will slowly pick up speed,to about 45mpr and maintain this until I press the brakes. When coming to a stop, it is almost as if someone is pressing the gas peddle. Before coming to a complete stop, if put in to neutral the engine runs at about 1500-1800 RPM. I have backed off the idle screw as far as possible, but this issue still continues. Thanks in advance~ Mike.

Do you know how it works ? What controls it ?

Did you hook up a scan tool an check for DTC'S - diagnostic trouble codes ?

Cruise Control Description and Operation
Cruise control is a speed control system that maintains a desired vehicle speed under normal driving conditions. However, steep grades may cause variations in the selected speeds. The electronic cruise control system has the capability to CRUISE, COAST, RESUME SPEED, ACCELERATE, TAP-UP or TAP-DOWN.
The main parts of the cruise control system are:
• The powertrain control module (PCM)
• The function control switches
• The stop lamp switch assembly
The cruise control system uses the powertrain control module (PCM) to maintain the desired vehicle cruise speed . The PCM assembly contains a low speed limit which will prevent system engagement below a minimum speed of 40 km/h (25 mph). The PCM assembly is not serviceable.
Cruise control operation is controlled through the function control switches located on the multifunction turn signal lever. The cruise control function control switches includes the ON/OFF, SET/COAST, R/A (resume/accelerate). The switch assembly provides driver control of the cruise control system.
The stop lamp switch is used to disengage the cruise control. A cruise control release switch circuit and a stop lamp switch circuit are used. The stop lamp switch is mounted to the brake pedal bracket . To disengage the system the driver presses the brake pedal. The speed of the vehicle at brake actuation will be stored in the memory of the PCM.
With cruise control, the vehicle can maintain a speed of about 40 km/h (25 mph) or more without keeping your foot on the accelerator. When the driver turns off the cruise control ON/OFF switch or ignition switch, the cruise control turns off. The vehicle speed stored in the memory of the PCM will be lost.
Ignition positive voltage is supplied from the HVAC fuse, to the cruise control switch. When the cruise control ON/OFF switch is on, ignition positive voltage is applied to the cruise on switch signal circuit terminal of the PCM. If the driver has not pressed the brake pedal, ignition positive voltage is supplied through the stop lamp switch, TCC/Brake signal contacts to the cruise control brake pedal switch signal circuit terminals of the PCM. Cruise control is canceled when the driver presses the brake pedal. The stop lamp switch contacts close, applying battery positive voltage to the stop lamp signal circuit of the PCM. At the same time, the TCC/Brake contacts of the stop lamp switch open and voltage is removed from the brake pedal signal circuit at the PCM. When pressing the SET/COAST button on the multifunction turn signal lever, ignition positive voltage is applied to the set/coast switch signal terminal of the PCM. When pressing the R/A (resume/accelerate) on the control switch, ignition positive voltage is applied to the resume/accelerate switch signal terminal of the PCM.
When the cruise switch is in the ON position, and the driver presses the SET/COAST button, the PCM then checks to see that the cruise control enable criteria is met. If the cruise control criteria has been met the PCM sends a class 2 message to the instrument panel cluster (IPC) to illuminate the cruise light.
The PCM will inhibit cruise control:
• When the PCM detects that the center high mounted stop lamp (CHMSL) in not operating properly.
• When vehicle speed is less than 40 km/h (25 mph).
• When in PARK, REVERSE, NEUTRAL, or 1st gear.
• With low engine RPM
• With high engine RPM (fuel cut-off)
• When vehicle speed is to high
• When an over or under charged battery voltage condition exists
• Antilock brake system/traction control system is active for more than 2 seconds
If the PCM determines that any of the cruise control inhibit conditions are present, the PCM will disengage the cruise control. If the PCM disables the cruise control for an inhibiting event it will record the reason for disengagement in the Disengage Definition data file.

Do you know how to test electrical circuits with a DVOM - digital volt ohmmeter, looking at a wiring diagram for the CC so you know what wires to test , if not your best bet might be to take it to a qualified repair shop .

You have break issues, possibly a warped rotor, a bad caliper. From your description it sounds like your braking distance is very long compared to normal. A clogged or bad brake line on one side will do this.

possibly your abs sensor

Not by guessing over the internet
without the vehicle to look over

That is not an emergency brake, it is for parking only. Get this checked outby a brake shop or general repair shop ASAP, DO NOT DRIVE IT!

check the brake booster for a vacuum leak under brakes

I would check the front brake rotors to see if they are warped. Chances are that you normally press the brake pedal harder at 60 than you would at 30 and this would explain why it may not be noticeable at lower speeds.
Jack a wheel up and spin it slowly. You should be able to feel it drag through tge brake pads at some point during the rotation. Or use a screwdriver butted against the rotor as you turn it. You should have to move it in or out at some point to maintain contact. If they are warped the best bet is to replace them.
It could also be a wheel out of balance, a broken belt in a tire or atie rod end going bad but normally these would show up at other speeds. Hope this helps.

1. Place a clean shop cloth beneath the brake master cylinder to prevent brake fluid spills.
2. With the ignition OFF and the brakes cool, apply the brakes 3-5 times, or until the brake pedal effort increases significantly, in order to deplete the brake booster power reserve.

Fill the brake master cylinder reservoir with DOT-3 brake fluid from a clean, sealed brake fluid container. Ensure that the brake master cylinder reservoir remains at least half-full during this bleeding procedure. Add fluid as needed to maintain the proper level. Clean the outside of the reservoir on and around the reservoir cap prior to removing the cap and diaphragm.

1. Install a proper box-end wrench onto the RIGHT REAR wheel hydraulic circuit bleeder valve.
2. Install a transparent hose over the end of the bleeder valve.
3. Submerge the open end of the transparent hose into a transparent container partially filled DOT-3 brake fluid from a clean, sealed brake fluid container.
4. Have an assistant slowly depress the brake pedal fully and maintain steady pressure on the pedal.
5. Loosen the bleeder valve to purge air from the wheel hydraulic circuit.
6. Tighten the bleeder valve, then have the assistant slowly release the brake pedal.
7. Wait 15 seconds, then repeat these steps until all air is purged from the same wheel hydraulic circuit.
8. Repeat this procedure with the LEFT FRONT, then LEFT REAR and finally the RIGHT FRONT.
9. Fill the brake master cylinder reservoir to the maximum-fill level with DOT-3 brake fluid from a clean, sealed brake fluid container.
10. Slowly depress and release the brake pedal. Observe the feel of the brake pedal.
    

It's not coming out of overdrive when you touch the brake pedal because the brake light switch/OD shutdown is either out of adjustment or just plain bad. It's staying in overdrive at low speed and causing the shuddering. Replace or adjust the brake light switch under dash at the brake pedal.