Cadillac just started to backfire and stall along with fading when accelerating.

This isn't a tune up issue. To me, it sounds like the fuel pump is going. Have you checked fuel pump pressure? Also, has the check engine light come on?

What you're describing, especially the 15 miles, is exactly what happens when the sock on the pickup in the gas tank gets plugged or is collapsing. When it gets bad enough for the engine to stall, before you try to restart it, remove the air filter cover, then work the throttle by hand to see if there's two nice solid streams of gas squirting in. If not, suspect that sock.

A poor man's trick to prove it is to remove the gas cap, remove the incoming fuel hose from the fuel pump, then use compressed air and a blow nozzle to force air into the tank. That will push the sock off the end of the pickup pipe. You'll be left with just the filter in the carburetor but the running problem will be gone.

At that point, if you don't want to drop the tank to replace the sock, you can cut the fuel line before the pump and install a Chrysler filter. Those last the life of the vehicle and you'll likely never have to replace it again.

Hi Jacobandnickolas. Didn't mean to butt in. Didn't see your reply before I started typing.