I think you are in for probems with this truck. Getting something that has problems is setting yourself up for continuous problems. I'd try to move up to a Dodge Cummins Turbo Diesel. A 12 valve of about the same vintage would be hard to beat. Go with a 5 sp manual trans. It's much easier and cheaper to repair a clutch or man. trans than the auto. The 12 valve has mechanical injection that is very easy to service and to adjust for more power if you need it. Plus they start in the winter.
I've got 270k on my 24 valve with minimum problems. It would pull 15k very easily. My own trailer weighs 12k and I pul it easily and get 13-15 mpg with it.