5.3 ran, but now it won't - sort of

[OKGMC4]

It's been running but the start has been getting harder. You'd have to turn the key a couple of times and it would click, then hit. Now it clicks and won't hit even with multiple key turns. It turns over great if I unplug all the injectors. Locks up again when you plug them back in. The couple times I did get it started it backfired but ran. Smells rich. Somehow this is fuel related. Just no idea how to tell what. Could a faulty pressure regulator be dumping too much fuel? I could see bad gas not letting it run right but not making it stop turning over. I wouldn't think all the injectors got stuck wide open at the same time? Any ideas? Please?