ORIGINAL: BuzzBomber

Nitro cleaner works well, it's just expensive, IMO. Acetone is great for cleaning on a part by part basis, but I wouldn't use it to clean the whole truck. It is more caustic than necessary and attacks some plastics.
I do keep a spray can of nitro cleaner around for when I just want to quickly get the major grunge off. When I do a complete cleaning, I usually start by blowing the truck off with an airgun. Then I spray it down with my home made cleaner(1 part simple green, 2 parts denatured alchohol) from an old windex bottle and let it soak a couple minutes. Then it gets a quick blowoff again, a quick mist of WD40 and a final blowoff. This works for me, others may have better methods for their own use...