The regulator is the smaller box. It's not typically the problem, unless it is actually broken. The DUVAC is the problem (large blue box on driver's fender). It's not really a "converter" box. Each alternator is 28V, but one is regulated down to 14V to charge the 12V side of the system as needed. Problem was it didn't work, so the front battery got undercharged, the rear got overcharged and their lives were shortened. It is debatable whether the military fix did anything to solve the problem.
My personal fix, given everything else is working properly and wired correctly is to switch the red and orange wires on the DUVAC box (orange to front post and red to rear post). This forces the top alternator to run in 14V mode all the time and the bottom stays in 28V mode. You end up with a split system, but it charges the front battery properly. You can also switch the top alternators internal regulator to "low" when doing this and it might be a little easier on the alternator. I sold my truck before I could actually try it, but TacticalTruck reported to me that on a long drive, the alternator belt got hot. Not sure if it's related or not, but setting the regulator to low should reduce the work on the regulator circuitry and alternator field circuitry.
Another thing I found was that after using the headlights, if I left the toggle in the "Service" position, it seemed to cause a drain on the battery as well, even though nothing else was on. Always turn that master toggle off, especially if you ran with the headlights on. That was my experience anyway.