Trouble in the Heat. Please advise

[phlegm]

Issue: I was driving about 30 min today on the interstate, got off the exit ramp, no problem. I made my left and started through the gears (3spd manual). in 2nd when I got to maybe 2.5 RPM the truck started to loose power and then surge back. I pulled off and drove around a lot for a while. at low speeds there is no problem, I can go through to 3rd @ 30 mph. When on the road and at higher speeds that is not the case, and it started the same thing again. when I got back to the interstate and it did on the on ramp, I noticed that when I pushed the accelorator my RPMs were not climbing. I held it down and once everything caught up on the interstate, it was 60 mph the whole way. then when I exited to go home, the same issue came up again.

Environment: I drive the vehicle on the interstate about once a week, usually not that far, but speed is not an issue and this is the first time for this. It was the hottest it has been in 13 years here today, we broke 100dg. and the truck has been local to this area since its original sale.

My Ideas:
Vapor lock -- I have limited expierence with this, only when I ran out of gas once @ 16yrs old. The heat makes me think of this.
trash in the fuel line or jets. -- I only say this because it happens at the top of 2nd and 3rd (until I level out). It could be when the 3rd and 4th barrels come open, if they are gummed up.
overheating on the manual tranny -- Oringinal thought, but the fluid was new when I checked the other day so vescosity breakdown is unlikely, plus with the RPMs not moving while trying to acclerate that leads me to the fuel system.

Again I am new to wrenching my own please help!