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Where to begin with this issue. Im working on a 99 Sierra 3500 5.7. The short version of the story is the truck ran fine then it was parked wouldnt start the next day. I cranked the crap out of it with about half throttle and got it to start. It ran like crap for awhile them smoothed out. Shut it off started fine 2 days later. Used it parked it and again no start. I tried the same as previous but it wouldnt start. No codes. looked in saw fuel in intake so i replaced the spider. Still no start. Pulled the plugs some flooded out some dry. Replaced all plugs cap and rotor and it started barely. Scantool showed missfire. Checked compression had 185 +/- on all cyl except 2 it had 5psi. checked intake valve not seating. Pulled heads had them rebuild and cleaned now have 185-190 on all cyl. Put it back together and it fired first try. It ran fine for about an hour in the shop so I put it to work. Drove great for an hour and then just died wouldnt start. Towed it back and it sat for about 3 hours. I cranked it and it started it was a little rough but cleared it out and it was fine. Let it run in the shop for about 30 mins then took it out myself. It ran great then after about an hour it bogged down then died. Hasnt started since. New parts include plugs,cap,rotor,injection spider,intake gaskets,crank sensor. Swapped parts include coil,ign module, distributor. Any help would be great I almost have a hole through the wall i have been beating my head against. Truck has 64k miles on it and prolly high idle time. Its a plow truck and has been fleet maintaned. Fuel pressure is 62 psi pump running and holds 60 off. Doesnt move while cranking though.
 

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Are those fuel pressure numbers taken when it starts and runs fine, or were they taken at an occasion when it would not start? When my 2nd fuel pump went out, it behaved somewhat similarly to yours. Fuel pressure was normal when it ran normal. When it wouldn't start or when it would start and stumble, the pressure was running low (45-50 psi).

When it won't start, can you get it to start on starting fluid?
 

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Do you have a strong spark? If not I would look to the ignition module or crank sensor. The symptoms you describe make me think the problem could also be heat soak related or an electrical issue on the power/ignition side. I would verify the battery connections and grounds to see if one may be dirty , defective or loose.
 
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