1992 Chevy Astro tbi problem

I replaced the pump with an a/c delco replaced filter and took throttle body off and rebuilt it and injector plate so everything is clean and rebuilt the vehicle runs great actually when it runs my fuel pressure right where it should be 13-15 lbs by the way te tbi was filthy I hve given it a complete tune up and since then I pulled a couple of plugs and they are firing correct so now that the histoy is done my problem is that it starts and runs greatit will run anywhere from 20 minutes to 3 days then it stahls I get spark but what happens is that no fuel is getting to the injectors and it always does it where I cannot check fuel pump but after anywhere from 10 to 30 minutes it will start right up and runs great I have been in a car wreck over 3 months ago and need to see doctpr couples time a week and have not been able to last 3 weeks for my injections this is our only car now and I am at a lost what the problem is so any suggestions would be appreciated and I cannot afford to pay for the help thanks russ