I think I read in a much older post about different oil weights for towing. I currently run Mobil 1 5W30 in my Tahoe(per owner's manual and the oil cap), but seem to remember a suggestion of running 20W40 for warm weather towing. I was thinking of swapping in 10W40 (kinda in the middle) for a little more viscosity, but not quite sacrificing the fuel economy. I've read through most everyone's threads on Mobil 1 vs. Amsoil vs. Royal Purple, I'm just wondering about the weights. Anyone have any recommendations? Thanx. P.S. Has anyone installed an aftermarket tranny temp gauge? My Tahoe didn't come with one.