Surge and bucking when coasting a few seconds between 5th and 6th gear

[morepower02]

Posting for a friend that is not on the forums. He recently purchased a 2011 6.7 with 94k on it. More noticible towing but there when empty is when in sixth gear and let off for a second or more the truck will shift to 5th and buck twice and the engine gives a rattle sound for a second. Normal?? I advised him to see if there is any reflashes needed. Any help would be great as either him nor I are up to date on 6.7 trucks.

 

[CATDiezel]

Stock or Free?

 

[morepower02]

Stock or Free?

Stock

 

[WHY NOT]

What speed is he going at and letting off to get it to down shift?

 

[redneck1]

Don't know what's he's done so far. Change fuel filters, air filter, put fuel from a good station. Have saw people change just the top filter because the fuel pump filter on the bottom was too much work. The rattle sounds like rail pressure spike.


KCCO

 

[morepower02]

Seems to be anytime in sixth gear. If you coast for a second or two and get back into it when it shifts down it stumbles and the engine lets out a rattle for a couple seconds. Runs great otherwise. Not knowing history will start with fuel filters.