Ok, So I just joined the forum because you are the only people who sound like you know what your talking about. With that said, Here's my problem:

2001 Chevy Blazer 4.3L V6 2x4

This is re-occurring issue and it doesn't seem to matter if my enginge is warm or not. When I first start off to work in the morning, as soon as I reach 2500 rpm, my tachometer jumps up and bounces around 3000-3500 rpm. When this happens, I feel a slight loss of power, but it still accelerates, just with less power. Through-out this, it will eventually shift to the next higher gear and be fine up to about 2500 rpms where the whole process repeats. Now, when I am at cruising speed, (Let's say [email protected], as is the limit on my tollway - Yay high speed limits!), sometimes it will start to bounce a little, say 2000-2200 rpm), when this is bouncing like this, I can feel the A/C also looses it's coldness, (maybe compressor not spinning, belt slipping, I don't know...!) The most recent codes I checked were for a crank position sensor and an O2 sensor. I plan on replacing these, but I doubt that those are responsible for whats happening.
PLEASE HELP ME YOU ALL-KNOWING GURUS OF GAS GUZZLERS!!!

Also, Just thinking, I'm not sure which sensor it is, but if it is my lower O2 sensor, before my cat, could that be causing this?

Also, the same is happening when I am in neutral or park. 2500+ rpms and the needle starts to bounce. So, maybe not a transmission problem?
Please help!

I would bet your throttle position sensor (TPS) is bad

would there be a way of testing the TPS to see if that is the problem, Or would replacing the part be my only option?

This may help you with testing
http://www.ehow.com/how_4489318_trou...ps-sensor.html

Also a quick search for "test+tps" with the author of "swartlkk" which would give you the information specific to these vehicles.

From the first search result:
Further information available in other threads that are detailed in that search.