nothing wrong with the 5.3. However a $750 motor would have higher miles, or be '' imperfect.'' Personally, If I was in your shoes, I would save up for a built motor. like a forged 11.0CR 408ci with a nasty cam. the 4l80e is going to eat allot of the power the 5.3 makes. I think when it comes to motor and cam swaps, go big the first time. unless its free, or dirt cheap.