I have been running the Mobil Drive Clean Plus HM Blend in 10w-40 for the past 2000 miles. Have driven the truck like a wild Indian going to crap (90 mph in Atlanta traffic!!! on 4.68 gears ) and have done a lot of 5 mile trips as well. Now I think the 40wt oil is a bit much for this motor. It only holds 4qts with the filter and revs pretty high (at least to one who is used to a '72 Chevelle) and works fairly hard. What i am looking for is a 30wt oil of some variety (GC is hard to find here) that has a pretty high viscosity at temp but is lower than a normal 40wt oil. I have thought about a 3:1 ratio of M1 10w-30 and 15w-50. I have thought about Syntec 10w-30 Blend. I have looked at the various HM oils, and I just dont have a feel for which is best. i will be driving the truck from Charlotte to Pittsburgh through the WV mountains so I want something pretty stout in the additive and film strength departments. Truck has 102k , automatic, 4x4, AC (will run ) new tranny fluid, plugs, air filter, etc Thanks guys!!