I have a 4.3L and 700R4 w/ shift kit in my truck. I've got no cat, flowmaster 40 muffler, EGR removed, injector pod spacer, hypertech "salad bowl", and K&N filter, and electric fan. Timing is advanced 8 degrees. I towed a car on a trailer weighing 6000 lbs total from Wichita Kansas to St. Joseph Michigan. It took a while getting up to speed and climbing hills would sometimes cause it to lose speed but I was able to get it going 85 mph through Chicago. 4.10 gears would help a bunch. So would a V8 with more torque. I tow a 19 foot cuddy cabin boat with mine too. It does fine. Not a race truck, but pulls fine. I had a 2013 Ram Hemi that pulled better but it also cost $42k and had 390/409 hp/tq compared to this 4.3L 160/235 hp/tq. I got rid of the Dodge and kept the GMC because the GMC is paid for and is cheap to maintain. I miss that Dodge but not the truck payment and since I don't have my big boat anymore I didn't need to pay for a truck that just sat in my driveway and was hardly driven.