fuel pressure is very important and even a little low can cause problems but if this has the newer distributor design then that is were i would start they are prone to failure and they will not quit running just run like crap because the distributor in the newer second design vortec 96 and up on the 4.3 is incharge of the injectors not the spark and the computer has default programming to keep the vehicle running but it will be slugish and stumble and hesitate basicly run like crap.

 

Well I put new intake gaskets on and I've been driving it around for 2 days and put some decent miles on it and no hesitation or anything. It runs perfect with the exception of the fuel pressure bleeding off when the pump isnt on so I'm gonna say the check valve is bad but the hesitation problem wasnt due to fuel pressure but a vacum leak under the intake. Looks like its all fixed and I will be unloading it asap I'm done with this nightmare, thanks for the help!