OK my experiences are with the earlier TH350's, and other (older) trannys. But we were
always able to influence the shifting by either changing the converter, and valves for
higher stall speeds, or with the modulator valve. From my perspective, it sounds like
you're pulling too much vacuum on the (modulator) valve. Maybe relocate the vacuum
line closer to the carb, or just put a clamp on it, and see if it influences the shifting.
The valve may even need replacing.
--Chris
No modulator, 700R4 shares some design with the TH350 but pressure control is not one of them. Seen many 700R4 transmission damaged due to someone adjusting the T.V cable wrong.
