Injectors:

I have a 1991 Chevy pickup, 350 automatic. I can start the truck, it will run for a bit and die. Are my injectors going out? the day before yesterday, it ran after about 4 starts and it was fine yesterday, but today it will just start and then die again. I replaces the fuel filter and about 4 years ago I replaced the fuel pump. Help!

Haulin68

Welcome to the forum!!! How many miles are on it?

I has 221,000 miles and the motor does not smoke a lick. It has been a great truck and I take very good care of it. Just can't figure why it will start for a couple of seconds and then die. I have been looking around on here and maybe it is the relay. Does a 1991 have a relay and what does it look like?

Sounds like it could be your filter.  Four years might have plugged it enough or maybe your fuel pump.  If it is your injectors you can try 44K. A guy on here told me about it and it really helped my truck run better.  
 http://www.bgprod.com/products/fuelair.html

Here is where you can order it online.
 
http://shop.autobahnpower.com/products.asp?category=BG%2044K%20and%20BG%20Products&product=BG%2044K%20fuel%20injector%20cleaner