BUT, if you're doing freeway miles, no problems. Doing city driving pulling local grades in the 15-25+% relm. Then the tall first year of the th400 and 4l80 get heated up really fast and quick. Whether you have an external cooler or not. That's the issue I have towing when I tow. If it's not geared over all low enough, Ive stalled many a truck out, even a 12k loaded 454, 4.10 th400 geared rig.