2000 Chevy s10 surging 2.2l auto

I have had some air conditioning work done on the truck. But the real problem is a little more complex. The truck seems to surge or sputter at certain speeds. If I stay below 40-45 there is no problem. When I hit that magic number the car sputters and surges till I reach a higher speed or reduce speed. I also noticed a similar problem at 50-55. I replaced the compressor, but still need to replace the evaporator. I was wondering if anyone else had similar problems or have heard this before. Thanks any help would be a mind helper. :banghead:

have the tp sensor checked out it may have a dead spot. you need to use a scope or something that will give you a graph to test it. you can try a DMM or volt meter but its had to find a dead spot with these.

Well looks like one of the clips that attaches the line from the transmission cooler was leaking cause a slight slip in the shifting. I appreciate the help. I am hoping that will be it. But you never know when you own a s10. Todd