Did the valve cover gaskets on my FIL's '03 1500HD today. 6.0/4L80E, odometer doesn't work but it's real close, if not over 300K. The last 2+ years the truck has been his DD, doing the same 35-mile (one way) all-highway work commute, then taking a terrible beating around the farm in the mean time - at least 25K a year. So far it's seen oil changes twice a year, mid-summer and around Christmas or New Year's, with syn blend Maxlife 10w30 and a Napa Gold 1522. In between times it spends as much time below the add mark as above it. Not too bad, considering.