Plus 1 on the Eraser/Wheel in a drill.
Depending on the age of the stickers heating them might not be viable.
I had some very stubborn stickers the body panel covers at my fuel tanks (under my doors) - i was able to remove SOME of the sticker but the glue remained behind, no amount of goo gone or aero paint prep would touch the glue.
a few minute w/ the Eraser Wheel in an electric drill and the glue was gone & the paint looking like new !