Matt, don't use a strap, bad things can happen if you do that. hit the rim in between the studs to loosen the bond between the rim, drum and studs. soak the studs with some sort of WD40 or the like and try to get it behind the rim. those are thick steel wheels...you're not going to hurt it by hitting it with a small sledge hammer, just hit it square and solid. It will come off...trust me. I have three of those trucks myself.
I do like Iowa 59's answere also. the strap idea will force the wheel to come off but also may jam it into the studs if it comes off crooked...you don't want that to happen.
