727 Trans Upshift and Kickdown Problems - School Me How to Troubleshoot

[RSI700VIPER]

I recently picked up a 71 RT Challenger 340 and the trans is not kicking down properly and is upshifting way too early.  Overview - Car is essential stock with no engine or trans mods that I can tell and 3.23 sure grip. Console shifter linkage is adjusted to factory specs.  Kickdown linkage is all original (3-section) and adjusted to hit the rear stop at WOT.  This was verified while car was on lift.  Problem - At low speed, say 30 MPH with trans in 3rd gear, if I punch the throttle, the trans takes about 3-4 seconds to actually downshift into 2nd, then upshifts into 3rd at about 3500RPMs even while peddle is still pressed to the floor.  Manually, the trans shifts fine with no slippage in any gear including reverse.  At this point, I'm not sure what to do next.  Check line pressure? Replace governor and/or governor spring?  Pull valve body??  Any help steering me on what to do next is appreciated.             

[Bullitt-]

  the video linked to in this old post may be a good place to start. As I understand it the "special tool" keeps the transmission lever pulled forward, not pushed back as you stated... I have read of folks doing it both ways but figure doing it the factory recommended way wouldn't be a bad idea.

Here is a Chrysler video showing how the system works and how to adjust the linkage.  You can watch the entire thing or fast forward to the adjustment procedure.(around the 12 minute mark) There is a special tool that holds the trans throttle lever all the way forward during adjustment.  You can rig something up to hold it or have someone help you.

https://www.youtube.com/watch?v=FY9WTWayCC8

[Mr Cuda]

The basics of lockdown adjustment is trans lever being held all the way back at wide open  throttle.
The first thing to check is the lever on the trans. They make a long, and a short  lever.
It is possible to have a mismatch in lever length,  ESPECIALLY if you have an aftermarket carb without the mopar throttle lever adapter..
Holley sells one, but don't care or know about carter or whoever makes the fake afb or abs now..I only use carter carbs that are factory,  on stock engines.
Obviously,  if you have a factory carb, check the trans lever.
After that, the line pressure could be set low.  Sure way to tell is kickdown disconnected,  next to no throttle,  your low speed upshift points.  Specs in the shop manual

[RSI700VIPER]

Bullitt - I've seen this video.  Very informative.  Holding the lever all the way forward is for adjusting the initial linkage setting and you can fine tune from this point.  Been there, done that.  I'm no where near fine tuning.  Holding the lever all the way to the back will (should) increase kick down and upshift pressure thus holding trans in gear at higher RMPs before shifting.  Thanks though for the link.       

[RSI700VIPER]

Cuda - I have the stock thermoquad and I'm 95% sure the kickdown lever is original to the car.  I'll try kickdown disconnected,  next to no throttle,  and measure low speed upshift point.  Pretty sure speedo gear is correct for 3.23 so reading from speedometer should be close.