Well...I took the plunge! Put Redline oil everywhere in my 2003 2500HD. I just clicked 1002 miles on the odometer. I will be sending the engine and trans fluid for regular checks and keep everyone posted on results. 5w-30 engine D4-ATF Allison 75w-90 Diff's I'm using wix filters and will be using redline grease for suspention components. I use my truck only on weekends for the most part(pull race cars to the track) so miles will come rather slow. 2003 Silverado 2500HD Ext. Cab 4x4 8.1L w/Allison trans 4.10 Locker ARE K Series Cap Rhino Liner Stainless Nerf Bars A work in progress!