Limp mode

Viper1

Ok so I put the K&M cold air induction and a Gemini cat back on the car. Ran great for awhile then the check engine light came on so I brought it in to the local Nissan dealer and they cleared all the codes. Get it back runs like a champ! Pulls hard, etc. about a 100 miles later it goes back into limp mode. Hardly able to do highway speed. You can floor it and it seems like the TB's are only opening 1/4 of the way. So I get the my destination was only in for about 15 minutes come back out thinking it was still in limp mode and runs like a champ again! Accepts full throttle, pulls hard, etc..... WTF! When it was in at the dealer they side the code was indicating "left bank"? Any help before making another appointment at the dealer?