Rebuilt tranny, now truck is backfiring/missinf at steady throttle?????

Just had the tranny rebuilt on my 97 Ram SLT 4x4 5.2, by a friend of mine who does good work, works/shifts awesome.. now the truck is missing and sometimes running bad..lacking power as well. Replaced the crank sensor and a little better but not yet fixed.. Have had thebefore cat front o2 sensor code for a while, could this make the truck miss.. Runs fine when you hammer it..

thanks for all the help