Delo is a great oil. Lots of Moly! Moly is good.
Your 2000 PSD came with green antifreeze. You can stick with the green or change to an ELC-> extended life coolant= less worring about. I think there are some Heavy Duty green coolants that are best, if you stick with the green. One that comes to mind is Prestone-Black Gal Jug, if you can find it. Any Big Truck Stop or Truck Supply Store should stock the Heavy Duty Green. Believe me all green antifreezes are not the same.
Might think about adding a Coolant filter, Bob at the Diesel Site has a nice system.
The 6.0L trans cooler is perfect for our 7.3L, ya might have good luck on ebay. The price has jumped up quite a bit, since the demand for them has rose. They will mount in the same mounting holes as the factory unit. Ya might have to change the fittings to a larger size? I can't remember.
Make sure you use a name brand synthetic in your rearend-->75W-140, esp if your going to be pulling that 5th alot. Check to see if you have a Limited Slip in that rearend as well. Ya might have to add a bottle or 2 of friction modifier.
If you use the Delo? you should be able to go 5k miles between oil changes easy.
Rotella or M1 Delvac are both top notch as well.
Congrats on your new Truck.