6.5 is acting like it's getting good fuel one minute n not another.
 

I have a 93 k3500 gmc 6.5. I drove it to my doc appointment and it ran fine. When I came out I started it and noticed by the sound it needed oil... no matter what I just can't get that under control.. ugh. All of a sudden it revved up then shut down. I tried restarting it but it wouldn't so I knew it had to be the oil. I walked over to the truck stop and got some, put it in the truck which it did need it and ever since then it's running as if it's bogging down then getting fuel. I can feel it as I'm driving it and it won't idle right anymore either. It has a new turbo as of 5 months ago and I always have a shop fix it. I just don't have the money for the shop anymore. Everytime I put it in there I'm charged over a grand and they lose bolts or don't tighten them or can't fix the problem without fixing other things first that wasn't the issue... and I've tried different shops. It's hard to find someone to work on my truck because it's extra heavy duty as it was a city work truck. This morn it started just fine, idled right then all of a sudden jumped around and shut down. Tried it again and the same thing happened.

PMD comes to mind..........:humm:

No PMD on a 93

I would look at getting the oil pressure switch replaced with an AC Delco ONLY!The OPS is what powers the lift pump on your truck.DO NOT use aftermarket OPS,they are usually bad right out of the box.
Then verify lift pump operation and repair/replace as required.
Then verify no leaks on the suction side of the fuel system including the sending unit-they have been known to rust through inside the tank and cause issues when the fuel level drops below the hole.

A quality vented fuel filler cap is also required and lastly make sure that the sending unit has a diesel fuel sock fitted-many aftermarket sending units come equipped with a gasoline sock/screen that has too fine a mesh for cold diesel to pass through efficiently.