I don't know what brand of oil you're using but I run 20/50 Amsoil in engine & primary, put many miles on running the same 20/50 in trans and did fine, but last year switched to 75/140 Amsoil in trans due to reading all the treads on here. My trans is now much quieter and shifts smoother too, not that it was bad before. Amsoil also as a 75/110 that they recomend for HD transmissions, I just used the 75/140 cause I had an extra qt. laying around for my truck.