1996 Vortec 5.7 wont start after sitting 6 months.

57vortec

replaced fuel filter and put fresh gas in tank. Just cranks. no start

0patience

So many possibilities.
But, check compression, spark and fuel pressure (with good gauge).
Fuel pump relay could be not working, could be moisture/rust on the plugs, could be a lot of things.
Until you check the basics, you are flying blind.

Mr_Shiftright

You could do a kind of minimal diagnosis by buying yourself a cheap spark tester at the auto parts store; if that shows a good spark, then you could release the fuel valve on the fuel rail (be careful--no smoking, and have a rag to catch the spray) very briefly, to see if fuel is at least getting that far.

These aren't ideal tests, but they would at least tell you, maybe, what's "missing". I say maybe because you could also have issues with the injector pulse being absent--in other words, even with fuel in the rail and a good spark, if the injector don't get their signal, the car isn't going to run.

Oh, you might also try a few squirts (not too much!) of starting fluid in the air cleaner. If the engine fires briefly, then you know at least that you have spark. You could then have a fuel delivery issue.