[WTO]

Looking for some ideas on how to correct line pressure flutter in 3rd or 4th over 1/2 throttle. Gauge bounces from 125-200PSI rapidly. I see it was recommended not to block the line bias valve, I'm confident that is the cause of my pressure problem.
Trans is in a 68 C2500, 4:11 gears and worn out 327. I have a 355 ready to go in but want the trans 100% 1st.
Valve body modifications were the transgo SK700 kit. I went back and reduced the boost valve from .500 to the next one down, .475 I believe. This improved shift feel but did not fix the line pressure flutter.
TV cable geometry is set up properly. The trans works/shifts perfect, without a pressure gauge you would never know there was a problem.