C12 help please

I'm out on the road with my company's 2000 FL Argosy that has a c12 and straight 10. I was headed to Sparta, KY and the engine lost top end power and acted like it was starving for fuel while going through the hills on I-71. Got set-up at the track and called a mobile service and he changed the fuel filters, finding a gob of some sort of crud on the filter. We figured that was it and would be good to go.

Left the track on Sunday and started heading toward Daytona. Truck ran great, took the hills with no problem, figured problem solved....Wrong. After driving 5 or 6 hours, it slowly started doing it again, to the point of me finding a T/A and having the filters changed again. This time nothing was found and the problem was still there.

We now have the truck at a shop near the track ( a Cat dealer) in Daytona but so far they are stumped as well. Truck runs fine for the first 5 or 6 hours after sitting over night. Absolutely no smoke coming from the stack, fuel tanks look very clean with no algae. Truck has 538,xxx miles. Truck starts right up and idles fine, goes down the road just fine, but once it starts stuttering/choking....

Once I got on 95 in Florida, I could slowly get it up to and set the cruise at 72-73, but even a slight overpass would cause it to start bucking and choking, and would continue until I cut the cruise off. Then I would have to slowly give it fuel until I got back up to speed. Shop is going to check fuel pressure, filters, etc., but I was wondering if anyone else might have an idea.

 

I have no idea and I won't be back to the truck until tomorrow. Picked it up from the Cat dealer with their clean bill of health. They said one fuel filter and the air filter were collapsed. No codes, fuel pressure was good. Replaced all filters with Cat filters, so we'll see. I took it on about a 10 mile test drive and it runs good, but as I said in my previous post, it didn't start acting up for 5-6 hours of driving. I guess we'll see when we leave because we are headed to an ag show in Illinois, so I'll have to climb Monteagle....