I just pulled this 150 miles today with my Tahoe. I estimate ~5100lbs and ~600lb tongue weight on the stock factory cooler, 3.73 gears and class 3 hitch. I struggled on one hill trying to keep 45 mph (dropped it down to 2nd) but otherwise kept it in tow/haul and 3rd. Transmission temps never went over 191°F and coolant never peaked 205°F.
For the occasional tow I think a stock Tahoe will do fine. I still plan on doing a trans cooler and they are cheap insurance to protecting your 4L60