Could it be my torque converter?
 

So I bought a 95 chevy k1500 with the tranny stuck in 2ND and 3rd back in july. Got the ecu replaced to have my tranny go out cause it was crippled from being driven in 2 and 3. I got a rebuilt 4l60e with 30k off Craigslist but it was from a '00 tahoe and put it in myself. My truck runs and drives great but the only issue Im having is if I give it a little to much gas when going to downshift into passing gears. It redlines for like 2 revs and then catches and accelerates normal. Could this be the torque converter? I have a new torque converter for the original transmission that came in the truck. I was planning on putting it in but I don't want to do all that work if it's not going to fix the issue. Could it be I just need to get the ecu flashed to get the tranny to the right shift points? I need some suggestions. Has anyone else had any issues like this?