Just replaced my transmission, before i got that done, 5 of my 6 pistons were misfiring. I was told that I need to replace my catalytic converter. Anything else I should look into in case that doesn't work?

 

I would't jump to the cat just yet.

More details are needed. Happens all the time (cold engine temp or warm engine temp).

All of the codes?

Tune up stuff is up to date - the 98 v6 still had a dist so the cap and rotor along with the wires and plus need to be confirmed.

Compression test on all cyl's shows what?