When driving at a speed of 20-25mph, truck will start to rev up and accelerate on it's own and when trying to apply my brakes,it resists and when I come to a complete stop the engine idles so high until the truck will jerk.

Cruise Control
Any given speed above approximately 22 mph (35 km/h) can be maintained with the cruise control by operating the lever.
-see photo

1. Accelerate and set: Lift lever briefly to set speed. Hold lever up to accelerate.
2. Decelerate and set:
   Depress lever briefly to set speed. Hold lever down to decelerate.
   Normally the vehicle is accelerated to the desired speed with the accelerator. Speed is set by briefly pushing
   the lever to position 1 or 2. The accelerator can be released. The speed can be increased (e.g. for passing)
   by using the accelerator. As soon as the accelerator is released, the previously set speed will be resumed automatically. If a set speed is to be increased or decreased slightly, e.g. to adapt to the traffic flow, hold lever in position 1 or 2 until the desired speed is reached, or briefly tip the control lever in the appropriate direction for increases or decreases in 0.6 mph (1 km/h) increments. When the lever is released, the newly set speed remains.
3. Canceling

To cancel the cruise control, briefly push lever to position 3.
When you step on the brake or the vehicle speed drops below approx. 22 rnph (35 km/h), for example when driving upgrade, the cruise control will be canceled.
4. Resume
If the lever is briefly pushed to position 4 when driving at a speed exceeding approx. 22 mph (35 km/h), the vehicle resumes the speed which was set prior to the cancellation of the cruise control. The last memorized speed is canceled when the key in the steering lock is turned to position 1 or 0.
Note:
If the engine does not brake the vehicle sufficiently while driving on a downgrade, the speed you set on the cruise control may be exceeded and you may have to step on the brake pedal to slow down.
As soon as the grade eases, the cruise controlled speed will again be maintained as long as the brakes were not previously applied, or the lever may be used to resume the previously set speed if the brakes were applied.


http://www.benzworld.org/forums/attachments/w202-c36-c43/153145d1197313761-pdf-owners-manual-w202-1995-2000-1999-c280_owners_manual.pdf

Further information will be required unless you would nlike a simple solution like.
Step one start said vehichle
Step 2 apply foot ti brake pedal and put gear selector in drive
Step 3 remove foot from brake pedal to accelerator pedal
Step 4 apply presure to accelerator pedal untill desired speed has been acheived
Note these steps will not work for manual transmission see section 37

For braking see section 22

I read somewhere that the problem was related to the sensor in the brake pedal, when it goes bad it confuses the computer, no input to indicate that the brake was applied, so it basically goes into limp mode, press the accelerator all the way to the floor and you get only gradual acceleration.

Does sound like the clutch is slipping

Trouble Code: P1336

CKP Sensor System Variation Not Learned
Possible Causes:


Set the parking brake and block the drive wheels for safety. Verify the hood is closed. Read the trouble codes. If a code is set, refer to that code. Start the engine. Allow engine temperature to reach at least 158?F (70?C). Then key off. Select Crankshaft Position Variation Learn procedure on Scan Tool & start the vehicle. Apply the brake pedal firmly and verify the selector is in Park. Increase accelerator pedal position until fuel cutoff is reached at the test rpm (e.g., 5150). Quickly release the accelerator pedal after fuel cutoff is reached. The CKP system variation compensating values are learned when the engine speed (rpm) decreases back to idle speed and the procedure terminates. Read the trouble codes and recheck for DTC P1336. If DTC P1336 runs and passes, the CKP system variation "learn" procedure is complete. If not, look for other codes. If no codes are set, repeat the test procedure.

replace your accelerator cable.

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!

Have you had the TPS calibrated? it needs to be set at a position with a specific resistance to set the correct idle speed, There is also no point try to do anything while you have the vacuum leaks as this make tuning impossible.

TRACTION CONTROL: An enhancement of an existing ABS system that prevents wheel spin while accelerating on wet or slick surfaces. It uses the same wheel speed sensors to monitor wheel speed during acceleration, but requires some additional control solenoids and a pump to apply braking pressure to control wheel spin. The traction control system brakes the drive wheel that's starting to spin to shift torque to the opposite drive wheel that still has traction. Most traction control systems only operate at speeds up to about 30 mph. Additional control strategies that some traction control systems use to limit wheel spin include reducing the throttle opening, upshifting the transmission, retarding spark timing and deactivating fuel injectors.

Hope helps.