The detent cable connects to the gas pedal, so it is the same for 2 and 4 bbl.

I suspect this is your issue. I did not use the TransGo springs; I left the original ones since I liked the factory shift points.

 

Some time ago (before i realised that my valve springs have been the issue) i swapped the governor that came with the car for a governor out of a chevy th350 (I once opened a thread about this topic) because the one that came with the car looked different than a regular th350 governor. Note that the springs are much wider than on a regular governor. I dont know if my th350 is the correct one for my car, since on the bellhousing is cast written 'Buick'.




Anyhow, today i pulled my "regular chevy th350 - governor" out and put the 2 yellow springs of the Transgo kit in which they claim for 'passenger cars'. I just wanted to be sure if my weird detent shifting and high revving issue is governor-related and it is. With the Transgo 2 Yellow springs at WOT detent, the Trans shifts @ around 4600-4700 rpm, which feels a lot healthier. Also have tire chirping 1-2 shifts when the trans kicks down from 3-1 .

when im gonna find some time, im going to test my odd Governor that came with the car again to check where it shifts with that one.

Lesson learned. Pretty happy now that i was able to solve this problem! Thanks a lot for all your help!