I'm glad you came to your senses and replaced your GMC with a good truck. In my humble opinion, GM has never had a good high-torque, low-rpm truck engine. Ford has had a long-stroke truck engine for I do not know how many years. When you tow, the low-end torque is what you are after. For me, I tow 4 tons of travel trailer. If I am flat, I will use OD all that I can. If I see that the transmission is shifting in and out a lot, I will disable OD. I have a 7.3 diesel with 4R100 tranny (is that right?) and 3.73 gear package.