BSwope,
As many others, I use Amsoil products exclusively. I run it in everything I own... lawnmowers, 4-wheelers, vehicles, compressors, etc. I've used several other products as well, however I like the protection and extended drain intervals Amsoil products offer.
Currently, I'm using Series 3000 HDD 5w-30 in my Cummins (actually have Amsoil synthetics througout truck), and have for nearly 10K miles. Once at 10K miles of use, I plan to get an oil analysis done to see how the 5w-30 and new EaA air filter are protecting my engine.
My fuel mileage, with no load and averaging between 60-65mph, is right at 22mpg. The addition of several items (Amsoil synthetic products, Rokktech sensor, cold air intake, Magniflow muffler, TSB flash, and EaA air filter) has increased my fuel mileage from 19 to 22mpg (all results were hand calculated). The Amsoil seems to be the biggest contributor to the increase, about 1. 5mpg. I used Amsoil in my 2001 as well, with similar results. It works for me!
Dwayne