I bought this truck a few months ago. Ran fine but had a hole in the tank. I replaced the tank, pickup/sending unit, lift pump, and fuel filter. Now it won't start. Lift pump turns on and primes. HP pump turns on and primes and the truck has fresh 93 octane. This truck will not start. Hits on 3 cylinders and shuts right off. If I use starting fluid it fires all 6 cylinders and dies. What am I missing. It's not ignition related because I have spark on all 6 cylinders.

 

So this is an 88 300 ci ? You shouldn't make us guess.
I would think you need to get a fuel pressure gauge and check. A pre - 94 300 EFI requires 45 to 60 psi to run. As opposed to all the V8's and 94 up 300's which only require 30 to 45.
That would be the first thing to check.

 

It is a 4.9L 300. I assumed they only made one 6 cylinder in 1988. I have a fuel pressure tester but i dont have the adapter i need to make it work. Ill pick one up and try again tomorrow.