I agree with the 75W-110 if you will be towing any.
While on the subject, what weight Severe Gear would you guys recommend in a 2007 Duramax 2500 Silverado with helical gear limited slip (aftermarket)? Truck has 60k miles on it and tows a double axle trailer when in use. They drive to shows all over the US. The guy who installed the limited slip put in Lucas 75W-140, which made all kind of noise in turns once the diff got hot. So he drained out the Lucas and has been running RP without issue since then, but cannot remember what grade he bought, except that it was expensive. He wants to change it now with 30k miles on the gear oil that is in there. I told him to get some 75W-140 because of the full-time towing and he has said he values protection over fuel economy. What do you think?
Sorry, not meaning to hyjack the good chef's thread, just need quick recommendation from others if possible.