Loosing Power When Accelerating At Operating Temperature

[RJ2003H2]

Hi, I'm the original owner of my 2003 H2, which has always been dealer maintained. I never had a major issues with this vehicle with the exception of this current issue. I'm experiencing power loss when accelerating from let's say 30-35mph to 45-50mph to merge in with traffic . The more throttle I give, the rpm's decrease, until I nearly have the gas pedal nearly pinned then it jumps into a higher gear. I've had this problem before and the Hummer dealer replaced 2 O2 sensors, seemed to correct the problem. A year or so later, same thing, dealer states it's the MAF sensor, replaced, problem went away. Recently I'm having the same issue, I bring it in to my local GM dealer, they put the scan tool on, no codes. Test the catylitic converter, passes. Test transmission seems fine. They can not give me a definitive answer as to what's happening. They claim it could be the torque converter, transmission, or catylitic converter. They won't committ to either one. Any suggestions? I really appreciate your help with this. If there is any more info you need, let me know. Thank you, RJ2003H2