I have a similar problem and I have adjusted the pump pressure linkage for both less amd more, by adjusting the length of the rod (which is connected to the throttle linkage). Here are my results:

1. Lengthen rod (less pressure) resulted in no flaring between 2 & 3 & 4th,
but slipping in 4th upon acceleration. All shifts occur sooner.

2. Shorten rod (more pressure) resulted in a flare between 2 & 3rd, however
no slipping in 4th when accelerating. All shifts occur later.

I am not sure there is a "happy medium"; I suspect my tranny is just worn.


Modulator pressure- a 1/4 turn at a time???:

"Try turning the modulator valve on the driver's side of the transmission clockwise. A search will tell you more about the modulator valve than you ever wanted to know If you're having trouble finding it, it's next to the neutral safety switch and has a vacuum line (should be black) going to it."

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1970 280S M130 engine- good runner
1971 250 M130 engine- #2 rod bearing, gone
1971 280SE (blown engine,parts car)
1977 German 280S W116-only 33 years old