My 96' used to start very easily, but since I hit 200k she needed a whole second. However, this last two weeks I have had to press the fuel pedal or she just cranks. . .a month or so ago I blew a fuel line (I am guessing it was the return line because the truck ran fine as the 5.46 a gallon fuel ran down the block). I bought a fuel filter but just haven't put it in-the current one is probably 12 months old so I was just going to do it to narrow the trouble shooting. Where would you go next? I am guessing fuel pressure is good cause it starts fine (with a black puff) with pedal.

 

If it has a return line leaking, it can get hard to start.
The line will allow air in ans usually doesn't leak fuel.
It is common to leak at the back of the head.

 

Try hand priming the lift pump before starting. It is easier to use a 24" stick and push from the topside. You will probably need to push it a lot, it is a very short stroke. If the hand priming solves the problem, you have a air leak that is causing the fuel system to lose prime.