My tow vehicle is a '89 3/4 ton van with the 999 with lock up (hd 904). I've had it for 11 years and towed locally and made a few trips towing out of town. It was still towing fine but started leaking bad out the front seal and it stopped locking up. Had it rebuilt while it was out for the front seal fix and put in a new converter.

Last week we towed to Elk Creek Dragway, about 70 miles one way and up and down a couple of steep mountains. No problems. It towed like a champ.

Race car and open trailer weighs about 4900 lbs.