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I don't think you will get enough flow through it to help much.
Ditto, waste of time.
I'll bet it's your radiator, every diesel I've had ran VERY cool.
The Cummins-Dodges right before mine ('89-'91; non-intercooled) had over-heating issues when being worked really hard because the radiator was a little too small. Swapping in a '91.5-'93 rad. fixed the problem.
If yours is partially plugged it's in effect has the same problem.
Bug screen.
Dakota I don't know how many farmers and ranchers pickups I've had in my shop that had either the fins on the ac condensor bedt closed by bugs or the radiator fins clogged by bugs and grass seed something very possible in the part of country you live in, just something else you might check it would be a cheap fix if you were that lucky.
Try usaing a plazma cutter. It worked great and gave a nice smoth line, A little paint for rust protection an a piece of door edge and you are good to go.