Fuel is one focus area.
The second is heat.
Once sure that the lift pump is pushing (clean) fuel, make sure that the glow plugs are working normally.
These items might not scratch the correct itch, but at lease we are stepping our way forward to isolate culprits.
By the way, my vote remains...
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While collecting parts from the NV4500, chances are good that the bellhousing will have a crack. Might not see it until after a good clean. So, have a backup plan of sourcing a new unit.
FWIW, there is an aftermarket kit for older Dodge diesel trucks which is a simple light and sending unit to indicate when the fuel line psi gets low (IIRC, 4 psi and less) which is also perfect for the 6.5 diesel. So, if looking to add a pressure gauge visible at the dashboard, will not hurt to...
Given the symptom of cleaning out the fuel filter, engine runs fine for a while, and looping back to cleaning out the fuel filter once the engine no longer runs fine again, my vote is to drop the fuel tank and check for whether it still has crud. Once confident that the tank is clean, we can...
Oh, and a while ago I had a little sports car and gave it to the parents as they wanted a spare car about the same time as I wanted to get an econo-box to save some money.
2 years later my work situation improved about the same time as my parents decided that they did not want a little sports...
Around my way, exhaust shops have signs stating that they will not do cat deletes (on vehicles that are supposed to have a cat) as the shop pays a hefty fine when caught. So don't even bother asking. They would rather turn down some business, than permanently go out of business.
Diesel repair...
Foundry date is likely low on the list of focus items when evaluating the engine. Unless, the idea is to go cheap by just running the engine and seeing if it lasts.
One way or another, HMMWV pulled engines commonly saw a hard life. Even sitting for years in storage is not overly kind. Were it...
To help limit creosote growth, an occasional flash fire (once everything is already good and warm) to burn the creosote can work. Same idea as a controlled forestry burn to prevent a larger fire. But, if the creosote is thick, then you will get the equivalent of a destructive forest fire.
So...
If only driving on flatland's, pick your poison. 5-er is certainly workable, but you will need to know how to keep things under control.
If looking to manage any grades, keeping the camper is arguably the better option. While I did not pull a 5-er or slide-in, I did pull a 30' 8K# TT with the...
^^^ This.
With the stated use of just "... a ranch truck ..." might work with using spacers for running wide treads, but the question is: why? Risk is messing up a wheel (maybe two) and possibly the hub just to save a few bucks. Oh, and the correct type of spacers are not inexpensive, so this...