[DK on the road]

We were off on a 4 week excursion. I stopped at a roadside rest stop for some sleep and in the morning the engine took about 10 seconds turning over before it caught and started.

 I'd never had this happen before. I walked around back, and all seemed good except my 382 Fuel PROcessor (large plastic) inverted Fuel filter was showing a little less fuel than normal. Normally its up about 2" but now it was 1" Not too weird, but a sign I should have recognized. I traveled about 200 miles and got into a series of stop lights and at idle I noticed it was running a bit rough and down at 500 vs 600 rpm normally. I noticed hesitating or stumbling on acceleration, so I pulled into a Hobby Lobby parking lot. 

On a side note, I get a bit of anxiety towing a full-size pickup and pulling into shopping centers with random cars, islands with tree's and possibly being forced to unhook and back out. On this day the God's were with me. I just got the coach circled around and pointed towards an easy escape route when it stumbled and died.

 I was not getting fuel. Now the 382 Fuel PROcessor had about 1/4" in it.  I first thought a lift pump was failing or a pressure relief valve was hanging open and washing 60 PSI fuel back to the tank and not getting to the injectors. I was in Twin Falls ID. I contacted the local Cat dealer; they said about 4-5 days out. Cat recommended the Freightliner dealer. Freightliner said if not their chassis, they couldn't do it. The recommended a local "Big rig" RV dealer, they don't do field calls. I tried Kenworth and Peterbuilt in town and each pointed fingers at each other and said they would do me right and couldn't themselves take care of me. I drove over to the original CAT dealer that I spoke with which was only about 10 minutes away in my pickup and spoke in person with the service manager. He suggested we order a lift pump from out-of-town w $134 freight bill attached to be in hand by 9 am the next morning.

The coach died at about 11 am, by 2 pm CAT surrendered and had a field mechanic at my coach. After several hours of pressure testing and trying out used lift pumps and testing pressures, blowing through fuel lines, pulling a vacuum on fuel lines, we found 2 things.

The fitting on the top of the fuel tanks had come loose enough to allow air to enter the system. This was only visible and found when I pulled the pretty SS panel that make my fuel tank look so nice, off to trace fuel lines and verify the "fuel check valve" was working correctly.  I was losing prime, because the leak was prior to the check valve.

I was on the road and out of Hobby lobby Parking lot by 9 pm. 

Occam's Razor= the simplest solution is always the best. When you here hoofbeats, think horses not Zebras (and unicorns). 

Well in this case, it's where I should have looked first because it was simpler than I was making it out to be.

I post my lessons learned, so that other don't make the same mistakes.
Post script, we did about 2,500 more miles without a hiccup.

[Richard]

Oh man, I was reliving my broken fuel dip tube from last year during the entire read. I feel your pain, this is such a rare and unique situation, that it is NOT what you would typically suspect.

So glad it was a simple fix, and sorry it was a tough diagnosis.

This next comment is intended to provide an easy diagnostic tool if you suspect you have a fuel delivery problem. It is NOT intended to be a hindsight remark on what could have been done. After all, without the help of a Good Samaritan, I would have gone down wrong paths on my issue.

The trick is to fill the fuel bowl with fuel, either with the priming pump or by pouring in some from the top. Then, with one person watching and another person cranking, watch the clear bowl. If you have an air leak in the fuel lines, you will get pretty large bubbles just above the fuel inlet.

I hope no one else ever has this problem. But if this trick helps you, then so be it.