Detroit Diesel 638 engine problem, please help

[KLUCAFIX]

I have a Hyndai HLD 150/Bering LD-15 truck with a Detroit 638 that has a strange problem. The engine starts and runs fine, but after few mieles when driving the engine develops a hesitation and looses power. It gets progressively worse to the point where u can only drive about 20mph after a few miles the engine shuts off, and it wonts to start, unless you whait few hours then the engine starts without a problem,
When the problem started you could drive normal for 100 miles normal, now its maybe 10 miles then its starts to losses power.
If u shut the engine off and let it sit a bit the problem goes away for next few miles.
We removed the fuel tank cleaned it and cleaned all the fuel lines and changed the filters and this did not help at all. We bought
a new injection pump and it alsow did not help. I'm not sure what to do next and was hoping someone may have seen this problem in the past and may have a solution.
Please Help. Thanks.

[Yukon6.2]

Hi
I would hook up a small tank of diesel as close to the lift pump as i could.Add a fuel pressure gauge and try it again.You could have a line were the inside is collapsing and plugging the fuel flow,either before the lift pump or after.
A fuel treasure gauge will help you see if the lift pump is making pressure when the truck stalls.
I have had a rubber line falling apart inside and the bits of rubber would pile up and form a plug either in a fitting or elbow and act just like what you are describing.Wasted a lot of time and filters finding that one.

[MaxJacob]

Thanks for the tip, man! I'll be taking note of this.

[cowboywildbill]

Way back years ago I had a pin hole in a fuel line on a Brockway Cab Over Tractor. It didn't leak fuel out but would suck air in. Had the same symptoms as you are describing.
Was a pain to find. Finally just replaced all of the fuel line.
Let us know what you find.