I think you've already heard all the really good advice, but there is one more thing that comes to mind that it could be. The fuel system on the '96 has a prefilter in the fuel thermostat/heater assembly. It sits just in front of your fuel filter on the left side of the engine. I guess it's possible that could be clogged if none of the other fixes noted cause the problem to go away.
I had the leaking fuel feed line problem on my '96 that caused the fuel system to lose its prime. That showed up as needing to crank the engine a long time before it started. Once started, it ran fine.
One other thing is the fuel cutoff solenoid. My rubber dust boot deterioriated and a piece of it jammed the solenoid actuator arm. The truck would sometimes start and sometimes not. I took the boot off and now about every 3 months I have to clean and lube the actuator or it will stick. If my truck won't start, the way I check that is to turn the key to ON and then give the solenoid arm a little tug. If it snaps into place, then I can start the truck and it runs fine. Sometimes if the solenoid doesn't get the valve fully open, it can cause fuel starvation when the truck is running. This doesn't sound like your symptoms, but I guess it's also a remote possibility.
