My 99 Silverado with 5.3L 2wd 170k miles chugs when I put it under load, but only when cold. It starts fine, idles fine, shifts fine, but put a little more gas to get it up to speed faster and she chugs and sputters. Once I've driven awhile and she's warmed up, all is fine. EGR looks fine, plugs look fine, MAF just cleaned... no codes showing either.
