t-350 trans oil press?

[rat trap]

will a manual valve body (in a th-350)increase line pressure at idle and low rpm.the reason i ask is because when using a high stall conv. i find there is alot of slippage when not hard on the throttle.i have tried 3different converters and found one that is just as efficient and the stock stall but with a 4500flash point.it goes the same mph as the stocker so i know its locking up on the top,but very slippery when light on the throttle until i get going.my belief is that a manual vb will increase line pressure at idle which in turn should lock up the conv harder at low rpm........what do you guys think?