Ok, here's the prob. Pullin my 16k toyhauler, when I get under heavuer load like going up a long hill I get a vibration which feels like a shudder.It feels like a fuel problem and I'm going to change the fuel filter. The big thing is that I can't hear it in the exhaust. I drove 175 miles yesterday no problem. Fueled and it started. Ran that tank out and have refueled, cetane and 2-stroke. I hope that does it with the filter change. Any other ideas? If not, I'm gonna have to limp it home. 400 miles.