I bought a sheet of OLD SCHOOL Diamond Back stickers for my restore. Well when I put them on they looked great, but they are peeling up. Why is this happening? Is there some kind of adhesive I could use to make them stick.
You've got two potential problem areas. NOS stickers are going to be iffy propositions in any case; the vehicle in the adhesive evaporates over time, from the edges inward, making it less aggressive and the sticker prone to peel up at the edges.
Surface preparation is the other question. It's got to be absolutely clean and as smooth as possible.
3M makes a number of aerosol adhesives with varying degrees of stickiness. I use their 'Super 77' in my graphics work, but I've used it on a lot of other stuff as well. If that isn't tacky enough, they also make a vinyl top adhesive that's a lot stronger. Of course, you've got to mask off everything with an aerosol.
Another possibility is a tube of 3M's automotive weatherstripping adhesive, popularly known as 'Yellow Peril'. It'd be easier to apply to small areas than a spray. It's bright yellow, so be sure to rub off any excess that squeezes out from under the sticker. Once it's set up a little, it'll roll right up like rubber cement.