I did the same thing and now have the exact same problem... I changed my 5.3 out for a ported 6.2 intake and TB. Everything was great I had the set of the pants feel too...I went on a 50 mile trip and the CEL came on with code P0171... Fuel economy is terrible now and there's some funny shifts in the trans and it's slipped a few times. I have a tune to begin with but put parts on after like a AFE CAI and Corsa CAT back... the CEL came on 60 miles after intake and TB were installed... How did you find the crack in your intake?