Boy, it's been a long time since I touched one of the old 4speed Hydramatics, but if my memory is accurate, the throttle connection is what regulates the line pressure in the trans.
More throttle, higher pressure, more clutch apply and firmer shifts. Less throttle, lower clutch apply pressure softer shifting. Misadjustment can cause too high pressure and harsh shifts or low pressure and slippage, especially when shifting or starting from stopped.
