Yeah, that budget is tough. I wouldnt sell mine for 10k, and its just a RC/LB, adn the injection pump could use a rebuild(and its a P7100).
If thats your budget, I would look into the 1st gen with the Cummins. The VE pump is very reliable. Its not capable of making as much power as a P-pump... these are off road rigs not sled pullers right?
I am contemplating selling my rig.....and getting something with a back seat for the kiddos....
I wouldnt bother a stock trans. The 47s dont like anything more than stock. You really need a good stout rebuild to start with. You can easily have 4-5k into an auto to make it reliable.
The other issue that I would be concerned with, an auto, behind a mild healthy diesel(or even a gasser), in a heavy rig, that will spend time offroad... is HEAT. You can boil that trans pretty easily. I would start with a good size trans cooler, and a temp gauge for the trans. Get messing around in mud or loose sand, and that thing will cook faster than, fast food....
Chase