I assume you have cylinder displacement down to V4 and you know about the flapper valve that a lot of folks complain about. We have V8 to V4 on our 2008 Tahoe Hybrid and my wife was complaining of the same stumbling the other day. So, I did an Oklahoma quick tune up on the vehicle. I got it up to operating temp and then performed several 60 to 90 mph runs in quick succession. Then I let everything sorta cool down to normal, although the temp gauge never moved up, and them performed several 20 to 98 mph (darn engine electronic governor) runs to continue the "tune up". When I got back to town and drove through town so I would have to stop at lights and stop sighs, I noticed no stumbling or hesitation at all. I was even able to climb a steep hill on electric motor only on the way to the house. That is the first time I'd been able to ever do that. The Tahoe is my wife's vehicle and she is a very "gentle" driver and hardly ever hits passing gear so it can get clogged up. I also put a half can of Berryman's B12 Chemtool in the gas tank which was about a quarter full before the "tune up". After I got through, I put a full can in the tank and filled it up with no ethanol fuel regular. I will add another can and a half of Berryman's to the tank the next fill up. A can treats 20 gallons of fuel. Sometimes you just gotta blow the soot out of them. But you have to find a safe stretch of road to do it!
