So I jack up my truck, remove the lug nuts, and I can't get the wheel to come off. I tried three wheels with no luck. Is there some special trick I need to do?

I had a flat about a year ago and the right rear came off fine. Now it's like it was glued on.

 

Give the rim a good whack with a 2x4 or something heavier.....there's probably just some corrosion holding it on

 

I did lay on my back and kick the tire several times. Would a rubber mallet be better than a 2x4? Is there anything to spray to loosen stuff up, but not mess up the brakes?

 

Loosen your lug nuts a couple of turns and roll up and down the driveway a few times applying the brakes. A couple of guys had to do figure eights. Use anti-seize during the reinstall.

 

Yes a rubber mallet would be much better than a 2x4.....or MAx's suggestion will work for sure.