2000 Chevy Astro fuel pressure

I replaced my fuel filter but I lose gas pressure at fuel rail after I turn on key. Van runs and I can drive it but I cant get any throtle out of it other than maybe 1/4 peddle and then it bogs down.With motor running pressure jumps up and down between 60 and 45 and with just key on it goes up to approx. 60 then goes down to 0.