my dad has a 96 gmc 1500 4x4 with the 5.7 vortec. On random days it wont start in the morning, it has plenty of spark and fuel but only fires on one cylinder every rotation but wont start, then when it does try to start it fires on the one cylinder then another will start to fire then another and you have to keep turning it over with the starter until it runs by it self. it has a bad misfire when it is running, plugs wires cap and rotor have been changed with new, also the spider/injectors have been replaced last year. the truck has 300xxx miles its a champ never rebuilt the motor,

 

Take the cap off and inspect the relucter wheel in the distributor. They can crack and cause missfire issues.

If that isn't it.... its time for an LSx swap!

 

If the truck has a stator on the distributor, that might be the problem. I had a similar problem with a ford 5.0 and the stator was bad.