If the truck already has the PMAX3, you won't need any more power upgrades. It alone will easily tow 11K.
SO vs HO doesn't matter all that much unless you are starting from scratch. If it already has a PMAX 3, why mess with it? The key here is whether or not it is the ADJUSTABLE pmax. Adding the remote (if not there already) is what you want to do, and only costs $100. This way you can keep the clutch alive by only adding as much power as you need.
in short, you don't need to really do anything to this truck. It's got an e-brake, a power module, and will pull very nicely.
If you no longer need the EZ, sell it. FOR THE RECORD, TST BOXES *DO* HAVE TIMING. It's just not as much timing as an EZ. You should be able to get enough money from your EZ to pay for some injectors, at least mild ones (275s).
You will probably find that your towing temps will be lower by using large injectors at a lower power setting on the box. Relying heavily on the box's fueling increases EGT.
If you want the ULTIMATE towing combo, go with some EDM injectors in a stage 2 or 3, and keep the adjustable box.
As for clutches, the HO six speeds have a little larger clutch than the SO six speeds. I was amazed to find that my stock clutch holds my Ez+DD2 combo (for now, anyway). If really towing heavy, the larger clutch of the true HO motors will be your friend, although the smaller clutch will shift a little better.
Ignore calendar years. Model years are all that matter here. There were no HO motors until MY2001. Check the VIN. These aren't like old Mopars, where there were model overlaps, and all kinds of one-off things. It's either a 2000 SO or a 2001 HO- no way around it.
I would recommend only using the GV unit when running empty.
Injectors will NEVER pay for themselves unless diesel goes to like $10 a gallon, and you use 275s. The additional 1-2mpg (max) is not a good justification for injectors. More power and lower EGT are good reasons.
As for injection pumps and the PMAX: Boxes are only hard on the pumps when you USE the power. So, if you set the box on kill and tow 30K#, expect very short life. Relying on larger injectors lets you run a lower level on the box, and take it easier on the pump.
***A fuel pressure gauge is the single most important addition you can add to ANY second generation CTD. ***
This guy is right: the 2000 HOs are VERY rare because they DON'T exist. .
Sounds like a good truck; have fun!!
HOHN