Bouncing rpms when accelerating?

Hello, I have an 05 Maxima and I just bought an 06 last week, pretty much planning to replace my 05. Had to drive it nearly 1000 miles to get home, at the very end of the trip, got CEL for p0420 and p0455. With my 05, I have thought it's tranny was going, it stuck in lower gears & accelerated quite poorly - my new one was great until these codes showed up and now it's driving EXACTLY the same. the rpms bounce when accelerating, and it just kinda feels and sounds bad. They don't both have the same codes. One thing I noticed in common on live data is that I'm getting little to no reading for the acceleration pedal. I replaced it on my 05, didn't fix anything, not sure if it's related, but thought it was worth noting. Wondering if anyone else has had the quickly bouncing rpms, knows what causes that? Any ideas would help