The only place I would look to for a rebuild is H&H Diesel in Fife. They are a bit spendy but you will never worry about it again. Probably somewhere along the lines of 3-4K for the whole job but like I said, you won't have to worry about it anymore. The other option is buying an engine from a wrecked vehicle. If you do that I'd recommend an upgrade to the 6.5L.

I've been in your shoes and had to bail on the truck because of the costs but I too sure liked that rig. Good luck.