I just replaced my a/c unit in my 98 GMC sierra 1500 5.7. Only when my a/c is on it almost seems like my trany?

is slipping, but when i turn my a/c off it runs perfectly fine. The parts i replaced are the condenser, liquid hose line, dryer and the compressor. I can't figure out why the a/c would be causing my truck to run rough. any help would be greatly appreciated.