Stalling cummins 8.3

Greetings! I wonder if anyone out there can help me... I have a 1996 Mechanical Cummins c 8.3. I have just recently replaced both fuel filters, the lift pump and the fuel pressure regulator on the injector in an attempt to trouble shoot low power. found a badly leaking CAC and had it repaired and "Wallah!" power returns! Changed the oil and filter and started a nice long trip. 600 miles later, the engine stops running down the road and have to pull over and run the Winn air purge and it starts right up. this happened several more times. I suspected the fuel shut off solenoid and wired it open... and it happened again! with the fuel cut off wired open, the only possibility would be an obstruction in the fuel line... but I can always purge it and restart it and it will run great for 10-20 miles. Every time its happened, it has been very shortly after going down grade using the PAC engine brake. Coincidence?? There is no connection between these 2 that I can see. the Fuel tank was over half full. I stopped and filled it up and it has not happened since I stopped using the engine brake... still coincidence?? I was above 6,000 feet elevation when it happened.
Any ideas or help is greatly appreciated! I am new to the forum.