95 grand prix se 3.1L; brake problem??

On friday, i just had my car in for a routine oil change and also asked him to replace my old brake switch with a new one i purchased. Because i was having problems with it.
Anyway, i got my car back and drove home, i noticed the brake pedal was stiff and sensitive. but thought nothing of it at the time. But now, when the car is running for awhile (warm) it seems like the brake is on more and more. So much now, that i feel like im driving with the brake on; One time i rev'd it upto 2000 RPM in drive and i couldnt move.
The parking brake is off. Seems to move when its car is cold.
Just called my mechanic, and he doesnt see how that problem is due to a brake switch. But he is super busy so i may have to wait a couple days to take it back in.
Any ideas what the problem is?
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pull up on the brake pedal... see if you hear some clicking.. the brake switch may not have been adjusted correctly.... Bobo

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