<VV> Powerglide shifting issues

[Joe & Lowetta]

I am looking for a little advice from the group on where to start on trying
to fix an issue with unusual shifting on my powerglide.
 
The car shifts from low to high at no more than 20 mph regardless of
throttle position and will not downshift above about 3 mph even if the shift
lever is moved to low.  If the car is started out manually in low and then
switched to drive, it will hold low up to about 35 mph, even if the
accelerator is released below that.  The shift is solid, but not harsh
regardless of speed.  
 
I have gone through the complete throttle linkage setup to insure that the
throttle valve is in the correct position in relation to both the pedal and
the carbs.  This made absolutely no diffence to the shift point, even though
it was way, way out of adjustment.  The adjustment procedure mentions
something about a detent in the movement of the throttle valve in the
transmission.  Is this something that you should be able to feel when
rotating it or just a description of it's function?  I could not discern
anything I would describe as a detent in it's movement.  Also, since the car
has only 79k on it, it has obviously spent some considerable time not being
driven regularly including less than 1000 miles in the two years before I
bought it.
 
Looking in the manual (yes I did read the manual), the troubleshooting guide
points to either the governor or the throttle valve as possible causes.
Does anyone have any advice on which is more likely to cause the issue
above?  I have no problem either taking apart the valve body to repair the
throttle valve or replacing the governor, just trying to avoid spending time
and money to repair/replace something that isn't broke.
 
Thanks for any thoughts you can provide.
 
Joe
'61 Corvair 4dr PG

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