Losing backpressure is always good.

Oversizing pipe causing too low exhaust velocity is bad.

LT's cannot hurt at all. Not sure what a "resi" is but if it's short for resonator, then what model is that?

LOL

I thought the current 6.2 GMC and Cadillac utilities were the only ones with a resonator.

Anyhow....ditch the progammer and get a real tune, no matter where. You'll need one with the ORY anyway.

What do you street race?