2001 GMC cranks but will not start on 2000 GMC Savana 3500

Have spark and turn on truck and fuel pump works and getting gas out of fuel filter. Engine will fire on either but not stay running

Asked by for the 2000 GMC Savana 3500
Got PULSE?....... Are injectors working? If it has fuel pressure and spark and will run by spraying ether or carb. spray into it , then maybe no signal to injectors?.....No air leaks between mass air flow and throttle body? That will also stop or greatly reduce fuel delivery. Do you have 2 vans both a 2000 and a 2001? your post has both years on it and if you do and they are both 5.7L , then maybe you can swap MAF and see if that does the trick.
4 answers
poss low fuel pressure even though you have some pressure you may not have enough to stsrt
Need to perform a fuel pressure and volume test with a fuel pressure test gage.
My guess is fuel pump is weak, need to know how much pressure it has!
JUST REPLACE THE PUMP! GM 11 years old, i bet that is what it is going to take to fix your truck!!!
Done been there lots of times. It can be off by 3 psi. and it aint going to run!