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Not sure of the problem

I have a 2000 mercury mystique and it has 91000 miles. I live in TX when driving to AL wich was 12 hours about 2 hours left to my destination my car started to lose power (not electronic power) tryed to push on the gas peddle to give it more gas but just slowed down but then shortly after it would allow it to speed up this would go on until i would pull over and let the car sit for about 2 hours or so. on the way back it happend again but in a shorter time frame now i cant drive for more then 2 hours strate without this happining but driving around town is fine. can any one direct me to what the problem could be?

Could be any number of things. What maintenance have you done on the car? If not a lot, start by replacing the air filter and fuel filter. That may get you going. Get the car to a local mechanic and have them look it over. You may need new plugs and wires, hard to tell.

The symptoms are typical of what one would expect of an ignition component were becoming sensitive to heat. Unfortunately, there are more than one possibility.

You should have (a) code(s) in the OBDII system. Many parts stores will downliad the codes for free. Have it downloaded and post the actual codes here.

Or, as Steve suggested, take it to your trusted mechanic for fixing.

Fuel filter.

Has it ever been replaced?

If not, now’s the time.

You may also want to have the fuel pressure tested.

Sounds like you have a partially plugged catalytic converter.

A forward O2 sensor could be the cause. It helps the PCM decide what fuel to air mixture is best when driving at a steady speed. You should try to read the codes and get a hint where to start.

If the fuel filter has not been changed on a regular basis then I might lean towards a failing fuel pump which has been killed over time by a partially clogged filter.
Fuel pumps can fail instantly and stay failed or they can be a hit and miss affair in which the problem may come and go at erratic intervals.

That’s assuming at this point there are no codes present, etc.