I have a 1994 GMC K-1500 P/U with the 6.5 L turbo diesel. I can start and drive the truck sometimes, and other times, it won't start or cuts off. Sometimes it will re-start, other times it won't. I have replaced the fuel lift pump, and have wired it to an "key-on" power source (in the case that my oil pressure sending unit is acting up) and I still have this problem. I have a Actron scan tool, I have a couple EGR related codes, and an IAT sensor failure. After searching for the EGR, I am now aware that the system has been removed by a previous owner. My IAT sensor lead is reading 145 degrees F when shorted (high according to the GM diesel manual). Because the truck runs quite well when it does run, I am not sure what the problem may be.

SOURCE: 94 GMC truck diesel starts,runs and then dies and will not start

I have the same problem and have trouble codes 35 and 36. I found out that there is a computer module that needs replaced as it sits low in a valley and gets hot and seperates. I am reseaching about the a/m fix that installs the new module away from heat.

SOURCE: 2004 GMC Sierra High Oil Pressure

if it is electrical oil pressure sensor I would start there. The best way to see if you have a major problem is to use a mechanical oil pressure tester. Take off the oil pressure sensor and put the mechanical tester on. The tester should come with a Gage. If it comes within your trucks oil pressure range than all is fine and replace the sending unit and see if that don't help your problem.If the tester runs high then the oil pump is bad or your cam-bearings could be the problem. But with cam-bearings you would usually get a low reading.

SOURCE: truck just shuts off

I own the same 3500 GMC 6.5 diesel truck with the same problem. We replaced the brain under the upper turbo hood and it fixed it pronto. No more shutoffs

SOURCE: 98 gmc jimmy loses power to a stop

the fuel pump could actually be malfunctioning. and the reason that you are able to restart and drive again is because when you turn the key on it is allowing the fuel pump to pressureize your system. but while the fuel pump is continuasly running it is loosing the fuel pressure. this is common on the cheap fuel pumps. i am not sure about were you got the fuel pump from but in all of my experiances with this problem i find that the fuel pumps have been boughten at a napa store.
i hope this helps you out.
and you could attach a fuel pressure gauge on to the fuel rail and start the car and watch the pressure to see if it is droping.

SOURCE: 1994 GMC Sierra 1500 6.5 diesel runs for awhile then stalls

check your pmd switch. i had mine changed and it runs great. the problem is that it gets too hot and burns it up. be sure to move the pmd swith on the firewall away from the injection pump.