Overheating issues

Good morning.

A radiator that cannot cool the system under load may be the issue. It may be too small. I would suggest getting a radiator that has at least one more core to add cooling ability.

I would go to a radiator shop and have them build you a radiator to fit your needs. Very common issue for towing with insufficient flow in the radiator.

Roy

I had a similar problem on a Ford 6.0 diesel, it would run fine on flat ground with no towing, but towing up one side of a mountain, I never made it to the top without overheating.
Come to find out the cylinder heads were raising up while under load and/or it was a EGR cooler.
Being this is a Dodge, I have to ask you did you leave any of the original parts from the old engine, such as but not limited to the degas bottle cap (if equipped), any oil coolers that may have been added on or for that matter any OEM sitting in front of the radiator and transmission cooler? If there is cooler, make sure no leaves are blocking the air flow and that goes for the radiator as well, make sure also there are not a lot of bent fins on any of the coolers, radiator etc and if you find any straighten them back out.
Replace the degas cap and also make sure the fan does run when towing or when the engine is jut warmed up.

Yes, it will. Three row will fit.

Roy

I am seeing they have two rows.
I see it does not have a degas cap, there is a radiator cap.
What about the fan clutch see if it is bad. If it is just a plain thermostatic fan clutch once the engine is warm and thermostat open, shut the engine off and then count how many times the cooling fan spins. It should only spin three to five times before it stops. If it just free-wheels, replace the fan clutch.