How about a clay bar?!
I've used a similar product to a clay bar for road tar and it worked great. Here is a link to the stuff, expensive, but the best out there, in my opinion. Actually, this stuff works like a clay bar, but is 100 times easier. GOOD LUCK!! http://www.autopia-carcare.com/ult-3200-3322.html
Wash it real good, then try a clay bar or a little bit of reducer. the big chunks should come off when you wash it. If that doesn't work try a sandblaster