sluggish response

[TheEdgeofSanity]

well, I went on a 300 mile road trip today with 3 of my closest friends and we had a blast. I didn't say anything to them but i really was noticing that my car was running poorly. Does anybody else have a problem with their car getting really sluggish after its been driven for over 30 minutes? My car does this everytime....it never overheats (my temp gauge never goes over the 1/2 mark) or anything and no lights come on, but there is a significant loss of acceleration and response to the gas pedal. It seems reluctant to shift to a lower gear when passing and has a rough feeling when applying more pressure to the gas pedal.

its really annoying because I've never experienced this with any other vehicle. Could something else be overheating which is causing this? i don't hear any weird noises or smells.