96 250 Power Stroke E4OD problem. I think

[Buckhangin]

Hello all, my name is Rick I have owned a 96 F-250 XLT 4x4 long bed extended cab since new. I am having a strange problem with the transmission, wanted to see if anyone else has had it, or knows what the fix is.

While towing my 18' fishing boat (1500 #'s) through the Sierra Nevada mountains I lost power to the wheels. I jumped out took one look under the rig and found tranny fluid running out on to the ground, and a solid line of fluid on the ground behind me for as far as I could see. Got a tow to my cabin @ Bucks Lake. I checked the tranny dip stick and found no trace of fluid. So I filled if back up with fluid, unhooked the boat, and started it back up. After a some slipping it went into gear. I took it for a test drive and it did fine, and has ever since. I have not towed with it since then (07.02.09)

What is the cause?

Do I need a extra tranny cooler? Change the shift points? Smaller tires?

I recently went to 315x75x16 Big O XT's tires from the 285's I had been running, besides that it is stock.

Any info would be greatly appreciated.