For heavy towing I would stay away from a 4l60, 65, 700r4, ect. Unless very light loads. You may not notice it, but there are much larger gear gaps in that transmission family than the 4l80e. 1st is way too low for anything with a little power, 2nd is lower than the 4l80, so you get into a spot where 3rd is too high and 2nd is putting you above where you want to be rpm wise. The only fix is slow down and putt up the hill in 2nd. Not really ideal. If you never tow heavy or never have hills you may not notice.