Possible tranny slippage

I would check the shift cable. It may have come disconnected either at the transmission or at the shifter. Good luck

Is the check engine light on, and do you have a code for an O2 sensor ?

It sounds like you shift solenoids need to be replaced in your tranny.

This is my drive cycle a generic drive cycle i have used many times over the years and it has never failed me most drive cycles are too specific and impossible to adhere to for most drivers follow these steps exactly 1. make sure all codes are cleared and no check engine light is on 2 make sure the fuel level is between 1/4 and 3/4 full (this is part of the enable criteria for the evap monitor to run ) 3 let vehicle set overnight 4 start engine and let idle until the temp gauge is in the middle (this cold start enables the evap monitor and runs the O2 sensor heater test )5 drive vehicle around town avoid the highway stay at below 50 mph and when stoping at lights remove your foot from the gas and coast from around 50 to about 10mph or less if possible this will run the EGR monitor after about 3 to five miles of this proceed to the highway or freeway and travel over 50 but under 70 mph for about 3 to 5 miles this will run the catalyst test provided the O2 monitors passed if they didnt you will have a check engine light on before this point also i do a coast down on exit ramps (no braking) they make great places to get that EGR to run ONCE YOU START THIS PROCEDURE DO NOT KILL THE ENGINE OR SOME OF THE TEST WILL FAIL TO RUN

Sounds like your transmisson is going, i had the same problem.

I would look at the ignition system. Possibly a faulty ignition module or coil ( if you have a single coil ) Multiple it will generally be one coil that goes bad and results in a misfire code. Or if it's the ignition module it might not throw a code at all, And it might test fine if it's had a chance to cool down before it's tested.

Your ac pulley may be worn so the engine needs extra boost and power to run it thats why when it is in optimal power (highway-- high engine power)as opposed to idle(low engine speed) it runs. You might need it replaced.

Since I work in government, my first question should be why would you need to go over 70 mph, but since I have a lead foot and a long list of speeding tickets on my record, I will keep my mouth shut on that topic. While cruising in the 70-80 mph, your transmission should already be in top gear, so you can probably eliminate the transmission. There are several possible causes of your problem including a vacuum leak, fouled plugs, bad spark plug wires, a dirty air filter, or a dirty fuel filter. Review your service records and see what has been replaced and when, then start looking at what hasn't been replaced. Sorry I can't be more precise without laying hands on it.

CHECK IF YOU HAVE THE correct size tire
open driver door locate tire tag and compare the size with what u have

the a/c condenser has a fan in front ( there is actually 2 fans if you sit on the car it will be fan on right side ) if this fan does not
come on immediately when you are parked and engine in idle
there is a problem with power to it, or motor failure. If you drive it
on the highway and a/c operates fine that's because air is circulating though condenser (thats what the fan is supposed to do at idle or slow traffic)