Bad acceleration after Rodeo is warm.

Hey,
I am having a problem with acceleration after the 1994 V6 Rodeo has warmed up. I step on the gas and the RPM go high but I get no acceleration. If I feather the pedal it does a little better, but I still can't get up the slightest hill, it is usually just enough power to get me home.
I just had a tune up done that included the plugs and plug wires, so it's not that. I also had the clutch replaced last year. I have just replaced the O2 sensor (which is what everyone said was the problem). I had the timing belt replaced last year as well. I get no check engine light or trouble codes. The other strange part is that I am trying to get it registered and it won't pass the I/M test because once they get the engine hot the h/c's jump ALL over the place. Normal is 220 I think and mine is ranging from 50 to 1200 at times! and this only happenes when it is warm (this makes me think it is a sensor, but which one?)
Any other ideas as to what could be causing the problem? Please help.
Thanks,
-Dustin

Check/clean/replace your mass air flow sensor.
G/luck
Joel

Check to see if your cat converter is plugged.
-Ryan