Stalling cummins 8.3

OK... WHEW! Well, I drove the coach ('96 Monaco Windsor) from Page to Bryce Canyon with no problem, not using the engine brake. Went from Bryce to Capital Reef on the BEAUTIFUL Hwy 12 and every steep down grade the engine stopped and I had to purge it with the Winn system to get it going. Thinking it still had something to do with applying the engine brake, I really heated those babies up on those 8% downs! even in 2nd gear! I barely made it to the Wonderland RV Park in Torrey. I talked with the owner who used to run a fleet of trucks and he said "guaranteed bad fuel filters". So I ordered some and replaced them. When I purged the system it acted like something was blocked. I noticed that a little bit of fuel was bubbling out of the new fuel pump aat the threaded connection on the suction side. I disassembled and used some good thread sealant and the leak stopped. I purged the system again and it still acted like there was a blockage, so it dsconnected every component and purged to see if if fuel would flow and find the blockage. I got all the way up to the pressure regulator that feed the return to the tank. everything was clear until I got to the return line and hooked it back up. I disconnected the return line on the tank and ran the purge... Blocked! So, I am now engaged in replacing the return line. I want to thank all of you who responded and hopes this may help someone else! THANKS!