Un driveable '02

[Scrappy]

My Father has an '02 3500 HO Cummins, He replaced the LP with a FASS about a year ago. After the FASS he was still having the fuel pressure issue and the associated codes for the VP 44 so it got replaced this spring. All was good until this week, it starts normally and runs fine for about a mile. After the mile or so it starts flashing the WTS light and stumbles(or the light comes on and the truck dies) it does this until it warms up to operating temperature then all is fine. it does not matter what speed it is going it will do it at any speed. He was able to catch a 1694 code once but the dealer can't recall it. I thought it might be a loose/ corroded ground and he is checking them out. What else could be wrong?

The last I heard from dad is that it is getting worse, the truck is undriveable. He also told me that that just prior to the light, it does the startup gauge check like something is losing power momentarily and then restarting the computer. I also told him to check all the connectors to make sure they are clean and seated but I haven't heard if that helped him or not (if he did check them then that didn't help)

They are getting ready for an 1100 mi. trip in the truck and really don't want to get stranded. Any help figuring this thing out would be appreciated by them (and their grandkids)