If you are tearing the cases apart this is easy. Just make sure to clean all of the oil passages and make sure to correctly preload the bearings. The preload numbers are in the manuals. When I rebuilt the NP200 in the M725 every single oil passage was plugged solid, and the preloads were way off. Im almost certain this what causes most NP200's to overheat. Since the rebuild, I haven't seen any heat problems with the 200.
The NP200 internals are too close in resemblance to NP205 internals, and NP205's don't have a problem overheating. Old NP200's with poor oil circulation (or no oil circulation) must be overheating from this problem. Add to the problem trying to spin them at high rates of speeds with 5.88 gearing and 34" tires will certainly cook at 200. The gear ratio you are running with those tires is much better.
Anyways, just my opinion.