I would stick with Meguiar's for all three steps... they vary in "abrasiveness" to a calculated degree. Substituting something for one of the steps will probably not hurt anything but you may be duplicating your efforts and there is a LOT of paint on that truck...

Independant of their three step process, Meguiar's offers a "Cleaner Wax" that I used to use to get the hard water spots out of my dark green CJ7. I worked with it in generous amounts over small areas of the paint at a time until I was happy with the results.

Meguiar's + Elbow Grease = SWEET lookin' truck. The best part is... six weeks from now when you hose off the mud, the mud will sweep right off the truck through judicious use of the sprayer on your hose, you can actually "hose the water off" of your truck as well! The only thing left will be a few tiny beads of water that you can pick up with a chamois or something.

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kjw & the
PNUTMNM

Blaming Guns for Columbine is like blaming spoons for Rosy O'Donnel