68GT, Walthers makes something called "Solvaset," supposed to be the most powerful decal solution out there--sort of the 16-inch guns of decaling. I haven't tried it, and at the point you're at, it might be better just to go with replacement decals, as others have suggested.
Alternatively, seems to me someone around the forum might have advocated straight vinegar for setting decals. I haven't tried that either.
Although I've encountered some pretty thick and unco-operative decals over the years, I haven't ever seen the problem those decals are giving you.