An old guy once told about those transmissions.

 

whats the benefit of the vacuum mod again?

 

That's exactly what I was thinking about when I was dropping the pan to shorten the pin.

It controls line pressure. At 0 inhg it gives you full line pressure and less line pressure under vacuum. = Nice firm shifts at WOT and soft part throttle shifts. It takes the place of the EPC solenoid so Line pressure is no longer controlled by the PCM.

Thanks for the info Vince. I did notice that my shifts seem perfect at about 175 psi. Thats what I'm shooting for. 200 psi fells like enough to break something.

 

UPDATE: I ended up grinding the pin down to 1.295". At 1.310 " my pressures were still up to about 195psi. At 1.310" it hits around 180 psi.

I also ended up peening the shift feed holes shut to about .086". Shifts are much tamer now.

The truck still shifts hard on a 3-4 upshift after kicking down to 3rd. This is at around 70mph while letting off the gas. I think the restrictor orifice in the boost/vacuum bypass valve is causing the modulator to react slow in this situation, so I'm still seeing full line pressure at 3-4 up shift while letting off the throttle.(just a theory right now). Everything else is great now.