I have the stock 3.73's, and 58K on the motor. I know I need to beef up the tranny but my first goal was to get more power for towing. I can't stand chugging along at 55-60 with my travel trailer (4500 lbs.). Even on a flat surface the thing stays at about 27-3000 RPM and in and out of downshifting. Basically I want it to tow better. I will contact the people you suggested in reference to the trans and see what they say. I pull the trailer about 5 times a year, but only because my Yukon annoys me while driving. If it towed easier, I would travel more. Thanks for the help and advise.