For the engine, tranny, frame, I put a 1 inch twisted bristle brush on my drill and went to town. Wire brushes to knock off the big chunks. When you get down to the metal, use the solvents and then high pressure....wash, rinse repeat....as many times. A standard wire brush on the drill for the sheet metal undersides....
I collected about 20 gallons of dirt/grease/crud mix when all done....I was amazed at the amount of stuff stuck to the underside of my truck.
