First of all, put in a good thermostat. Drilling holes in the thermostat is a mistake. If you're overheating there's another reason.

The number of rows in a radiator tells you nothing about how it will cool, unless you know the size of the tubes and the fin density. There are a lot of replacement aluminum radiators out there from Asian sources which have a multiplicity of tiny tubes and a dense fin structure. This is because people see "three row" or "four row" and think "better". These radiators are often more restrictive than stock radiators, and won't help you one bit.

I think your problem is that stump puller rear axle. Diesels build heat at high revs because that's where they will burn more fuel. Switch to a 3:54 and I think your temps will be fine.