I have a 94 chevy step side 2x4 with 31 1/2's all the way around with no lift. They fit fine on the rear but started rubbing on the front when I would hit big dips in the road at speed. A set of heavy duty front springs solved the rubbing issue by raising the front 2''. I did put a set of helper springs on the rear to help from sagging when I pull heavy trailers. My speedo is off about 3 MPH but my gas millage is still 16+ per gallon. It is a little sluggish in the hills when pulling a heavy trailer but I live in a flat area so it's not a big issue. It has the 5.7 throttle body and does run great when empty though. I wouldn't go over 31 1/2's without a gear change.