Losing BIG power in hot weather, Not overheating

Just took a short trip to Vegas in my 01 GT with the Girlfriend and Two buddys I work with. Im currently stationed here in San Deigo where i purchased the car and was very happy with its performance. Anyway, Heading northbound on 15 just outside of Barstow I noticed the bogging down or just running real sluggish, thinking it was just from running the AC, and the increase in elevation I gave it no second thought. After letting the car sit over night and half the next morning, car is still runing like poo! So after being pissed and nervous that the car would kill over and die on the drive home i took her real easy. I did noticed no change in gas mileage and wasn't overheating! Just South of Barstow the car just magicly comes alive and sarts running as if nothing had changed!!! Im stupid stumped and have no idea what could be going on under the hood when the temp on the streets rise! Could the cats be getting clogged? Is the MAF going bad?

Any advice would be great for the next road trip we embark on!
Thanks

No sir! My buddies drove seperate in a 06 Eclipse GT. Here at home i hold my own against his car, but in hot weather my car falls flat on its face! Even on a cold engine start at the hotel in Vegas it just didn't seem right.