Yeah I would start with a rebuild kit and clean that TB up. The vacuum passages get blocked up with crap and will cause all kinds of weird things. If you never have done one it is very simple - just make sure everything is really clean and replace a few gaskets. The kits also come with a new fuel pressure regulator.

 

I see that the booster does look rusty, but it seems like no fluid is currently leaking so maybe the previous owner had it fixed, does this matter or will it start to leak again eventually?

And ya Sham, i will be ordering a rebuild kit, any links to any good deals? I found a few but none with a fuel reg.

 

Both of these come with regulators:
Gp Sorensen/Throttle Body Rebuild Kit (TBI) (97-724) | 1989 Chevrolet C1500 1/2ton P/U 2WD 8 Cylinders H 5.0L TBI | AutoZone.com

Gp Sorensen/Throttle Body Rebuild Kit (TBI) (96-541D) | 1989 Chevrolet C1500 1/2ton P/U 2WD 8 Cylinders H 5.0L TBI | AutoZone.com

As long as the break booster itself isn't leaking vacuum, and the master cylinder isn't loosing fluid over time, then you're probably fine.

EDIT: I just looked this up under your truck, and this is the only one Autozone says will fit:
http://www.autozone.com/autozone/par...2053_298876_0_

 

It sounded to me like the battery and starter are OK and it's probably fuel related. One way to tell is to take the air filter off and have someone pour a little gas into the TB. If it fires right up I'd check to make sure the fuel pressure is OK. Another thing to try is turn the key on and wait several seconds before turning to crank. If it starts faster that way I'm sure it's a fuel pressure problem. Wouldn't hurt to run some cleaner thru the TB system.