Oil for Allison
I have a 06 Duramax, 130,000 miles and trying to get better fuel mileage. Going to do a tune, fix EGR, change converter on exhaust and add trans kit. I use amsoil in trans now and the guy doing the work would like to use super shift by amsoil and on amsoil website looks like ATL fluid would be better for my application. Not going race it or pull on a track just towing a 5000# trailer to jobsites. It was suggested to put on a 4" exhauts put not sure I would get a return of $600 on fuel savings and it would also be louder. Anybody have thoughts on oil and 4" exhaust?