Use a piece of monofiliment fishing line wrapped at each end around a "handle" such as a piece of wood, and "saw" the adhesive against the body of the truck. It will help if the adhesive is warm. Let the sun beat on it for a while, or use a hair dryer.
The adhesive residue that is left can be removed with a solvent such as 3M adhesive remover.
Wax the area well, and you'll never know there was anything there.
I removed all but the Duramax emblems with nothing more than a heat gun and a good pull. I also took off all the moldings to switch to the GMC chrome. I did not have any glue left anywhere with this method. Heat and yank.
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