Stiff springs in the back and tighten the feces out of your slipper clutch may make it wheelie. Also, try putting a ton of spacers on the back as well if you don't have stiff springs or put them on anyway if you do. I think, if you can tell it is about to wheelie, this may make it do it. You could also let it roll back a bit and then floor it, but this puts a huge stress on your drivetrain, as well as tightening your slipper clutch.

I would rather my truck stay on the ground though, because wheelies are just for show... But, if you have a big engine laying around, that alone should be enough to pull that truck out! Try an O.S. .18 CV-RX, TM, or TZ if you want that, but keep in mind you might have to do some drivetrain strengthening with the TM or TZ. I don't think the CV-RX will cause too many problems. Not sure though...