Certainly not questioning your friend's work....but I've seen top notch mechanics make mistakes before. I mean, you're tryin to diagnose somethin. The only way to properly do that is cover all the bases.
About the throttle pressure linkage. Proper adjustment is with the gas pedal on the floor, the kickdown lever on the transmission should be ALL the way back as far as it can go. If it's not, the adjustment is incorrect. ...and yes, the lever at the transmission is spring loaded. Lastly, a return spring on the throttle pressure linkage itself (not just the carburetor linkage) must be installed to pull the throttle pressure linkage back ALL the way forward. If it does not return all the way forward it can cause harsher than wanted shifts at part throttle.