[oil pan 4]

If you are even thinking about maybe towing 10k don't use the stock dodge auto transmission. The 47RE. Its rated for 450 ft/lb of torque. A proper 12 valve 5.9L can make 450 torques at idle.
Problem is the converter lockup slips constantly under load with the 700+ foot pounds of torque the 12 valve 5.9L can easily make.

With the manual only problem is the engine can make enough torque to strip the teeth off gears or spin gears on their press fit shafts.

Only answer is the ATS made upgraded transmission.
Which is only 7 or 8 thousand dollars.

Anything that says ATS = $$$$.
Cheap knock off of ATS products are just that, cheap knock offs.
Most if not all ATS products have 5 year 500,000 mile warranties.

Cummins manuals will give safe minimum safe speed and proper oil pressure for operation. The main thing with lugging the engine you have high load and low oil pressure. This causes rod bearings to go bad.
I would say rifle drill the crank, so the rod bearings oil passages get fully interconnected to each main bearing oil port allowing all rod bearing to be oiled through the full 360 degrees of rotation. Most cranks are drilled so each rod bearing gets oil from 1 main bearing oil galley for less than half the rotation.
But that doesn't fix the oil pressure problem at low speed.

Welcome to the diesel towing world. Things wont be cheap. Get over it.
Or you will find your self on the side of the road looking at a huge repair bill that will cost almost as much if not more than doing it right the first time.
If you want cheap stick with a metro.