I just traded a 03 z71 avalanche for a H3 Hummer. My avalanche came stock with a 373 rear end. 265 were the largest tire i could get on it stock. I actually put a fab tech 6 inch lift on it with 305 tires. Also put a hypertech on it and it performed decent with that set up but it sure ruined the ride and handling. Gas mileage was about 13 with that set up.Sorry it took so long to get back here. The truck is a 1500 Z71 5.3 with 4:10s.