Gear / Tranny Oil

[Curtisj28]

"They" say film strength is better in synthetic. But "they" say alot of things. I use mobile synthetic 50 in trans and 75-90 in rears. I change it every 150-200k. Probably overkill but haul heavy. Also can check for metal bits that way. 1.3 on truck and everything is original. As long as you regularly service I wouldn't see an issue running either. But in my application I prefer synthetic. Extreme cold and heat heavy 95% of the time 90-100k lbs. Probably just peace of mind.