I used to do asphalt work...diesel fuel is the way to go for getting it off...spray and walk away.....and watch it start to melt off...also WD40 works good.
Those trucks look good. I do Hazmat tanker work now, and the company I work for has a company come in on Tuesdays and Thursdays and wash as many trucks as they can (over 75 trucks and 250 tankers in all, but alot are all over the country). try keeping a 48' polished aluminum tanker shiny......along with 10 rims, tanks, 20" drop bumper, big open stacks ( to hear that CAT under the hood roar...and of course to have fun with the JAKES!!!)
There is nothing like a clean truck!!
MIKE