I had to lift off in 4th because of a hill momentarily, so that throttle closure is intentional

Added a Cobb downpipe back exhaust. The exhaust is dual 2.5" to a full 3" with no taper anywhere on the exhaust and it deletes the secondary cats. Car has felt slower and I have thrown CELs multiple times when pushing the car hard during spool up. Codes are always 2ABC and 3100. Was dead even pulling against a 5.0 with bolt ons and Bama tune when I used to pull slightly on a FBO w/ LTH 5.0 and professional tune. May just need adjustment or something.