The transmission is the weak link in any "heavy duty" diesel 3/4 ton or 1 ton truck. Don't believe that the Allison transmission is any different than the competition, as it's no better. They've just done a good P/R job with the name.
I would suggest you find a shop that can pull your current transmission. Then go to Tousley Ford online and order a Ford Heavy Duty rebuilt transmission for around $2200. They're by far the cheapest parts source, and they can arrange for transportation. The Ford unit comes with a 3 year, 36K warranty. You also want to go with a new torque converter.
If you wanted to spend substantial money, John Wood is the man on the west coast that stands far above any other transmission builder. You cannot tear up one of his transmissions.
I'm a fan of DP Tuners on a 7.3 engine. I've run a 60 hp tow and a 80 hp econo chip for many years, and have not had a single problem. And the truck is a very strong performer--fast and efficient. They use John Wood's transmission software.
A 7.3 diesel with a 3.73 axle ratio is a 13k maximum tow vehicle. The Pin weight should be more like 2500 lbs. max. If you've got a 15K fifth wheel, you're grossly over the capability of that vehicle. And if you don't have a 6.0 tranny cooler or a TruCool or B&M tranny cooler, you may have cooked your transmission by overheating it pulling too fast and thru the mountains.
Do not consider a used transmission, as the 7.3's automatic is a minimum of 12 years old. And unless a shop is completely competent with Ford diesels, don't consider having them rebuild your tranny. It's just not a place to go the cheapest way--not a good value in the long run.
