i would not use paint stripper. . . .
take some lacquor thinner on a rag and rub it on there might want to wet them up and then let it sit for a few minutes and then keep wiping with the thinner on the rag. . . . watch the cars paint though . . . .take them off first.
armour all them up after you are sone and they should look nice with a little time spent on the,
I would wet-sand them. Use a fine grit paper and keep the flaps wet. It will take a while, but the water will keep the mud flaps lubricated so you don't sand into the rubber as easily, along with only using a 600 (or so) paper.