I'm starting to have these issues as well. However, mine does this if I run more diesel/gas than I do wmo. Too much gas and it won't start at all unless it gets lots of either and it needs to rev over 1200rpm to keep from stalling out. Yet it will start and idle at 700 rpm with wmo. I know there's a float in the FDC (mine isn't bypassed), guessing it's gummed up and it's not adjusting to the density of the fuel because it did before and the changing of fuel filters made no difference plus it has a new in tank pump. I'm running cleaners in every tank and now the governor is starting to kick in like it's supposed to when I hit up grades and stuff where it wasn't before for a while, not all the time, but it's slow progress. I know parts can get gummed up over time, but this tells me, that FDC needs to be cleanish for that float to operate properly and can lead to lots of issues otherwise. I doubt this is the OP's issue, but it's an issue I'm sure someone else may have and don't even realize it.