hesitation in 1st gear

I did a search and nothing really matched my issue. Yesterday it was hot as hell...like 94 degrees. I drove my car around all day and it was fine. I parked it for a couple hours and when I drove it again it appeared to be idling funny at very low speeds (like 5mph) through the parking lot. It hesitates like it doesn't want to go into first gear right away. Then it goes into gear kinda rough, but not to harsh. The rpms don't jump way up,but it reves slightly. It has alway driven fine till this point. Could suddenly my tranny just act up out of no where like that if it was fine a few hours earlier? Could the heat and a lot of driving have something to do with it?

[DavieGravy]

Don't know if this will help but try loosening your gas cap. I too have this problem (intermittently) and I think it might be from excessive fumes in the tank. Heat causes this.

Thanks..It had to be the heat. I drove it around the parking lot last night and it seemed fine.