Have 99 sierra has spark and fuel to intake but wont start sometimes sputters but no go please help

What shape are the spark plugs in?

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

Could it have timing belt issue?

the first thing is check your fuel pressure for the right psi. some vehicles will not start if the pressure is off only by a couple psi. your particular van is epuipped with a injector module assembly under the upper intake manifold. commonly called a injector spider. those are notorious for leaking and will keep a vehicle from starting. also while your checking your spark how did you do it? if the spark was any color but blue it is too weak of a spark and the vehicle will not start with that. this could be worn plugs, wires or weak coil.

well spraying a little starting fluid into the air intake and trying to start it will tell you if it is fuel related or and elctrical problem, i guess that would be the first step, and narrow things down a bit, if it starts with the fluid it is a fuel issue, if not its elctrical.
check you spark plugs, if your fuel pressure regulator was bad and it was flooding the engine, it would have fouled your plugs, i guess id start with those two things and at least start narrowing things down.

Good Luck, come on back if you get stuck....

I have 1993 gmc 4.3 vortec v6 turns over but want start. replaced fuel pump, fuel pump regulator ,ecm, tps, coil

check for injector pulse and for compression

It may be the crankshaft position sensor needs to be replaced.Suppose to be above and behind starter ,but may be different location on your car. Here go to www.saturnfans.com to get more info very helpful site.

check out the injectors and the coil pack to make sure you are getting spark

Check the fuel pressure regulator. Mine was doing the same thing and the pressure regulator was the problem.

If it idles ok and only "sputters" under load it could be either an ignition or fuel problem. How long has it been since the fuel filter was changed? How about spark plugs and wires? Without the proper diagnostic equipment and the vehicle in front of me, these are the easiest things for the DIYer to tackle with the fuel filter being the cheapest option.