You might try naptha- regular lighter fluid. That is a solvent for many adhesives. Just be careful not to burn up your truck in the process. Depending on the thickness of the adhesive layer, you might have to soak the adhesive for a few minutes to soften it. I don't know if naptha will work in your situation.
You could also try a carburetor cleaner, Berryman's Chemtool, which contains xylene and tolulene, both of which are strong solvents for many solids, including paint (and your hands, too).
Harvester
