I assume from the subject line that this may be referring to a Subaru Eng

in a Vanagon,,, If that is the case then You have a VSS that either is not working

or is sending incorrect data to the ECU ~

> On 1 Feb , 2023, at 12:16 PM, John Rodgers <jrodgers113@GMAIL.COM> wrote:
> 
> What rpm should show on the tach at 70 mph? Mine shows 4000.
> 
> But, beginning at  65 mph the engine begins to buck as if doing a high
> speed on and off. Can't go faster. Is there some kind of engine
> governor that needs to be reset? I have been told I should be able to get
> 6500 rpm and above out of this engine. This has me mystified.