So I brought my car to the shop to have them install the new trans modulator...it's way to cold for me to sit outside and fix it...and I went to pick it up today. Shifts unbelieveable!!! So much better with barely a clunk at all. But they told me they didn't need to use my part, and that the guy who worked on it just fixed something else and made it shift better.

So after driving it, I pop the hood and see just what they did. The throttle vaccum line is now mounted directly onto the modulator without a check valve. Now I'm really confused because it made it shift so much better, but isn't this supposed to be bad? I'd appreciate any answers.

Maybe your vacuum line(s) in that area were just cracked. You're going to want to put a check valve on there. The check valve is there to bleed off boost.

yes he is right you need to put the check valve back on. The modulator should not see boost. I forget what the diagram looks like (its been a while since I looked at Jimmys FSM) The mechanic probably took it off since NA cars don't use them and probably thought someone put it on not knowing what they were doing. Someone removed Jimmys when he had an auto. The modulator valves were only made to see vacuum.
Tim

Yeah I have the diagram, and tomorrow I'm bringing it back to them. It shifted great for 5 miles or so, and now it's doing the same hard shifting so they're gonna be replacing the modulator and reinstalling my check valve.

Thats how my TGP was when I first got it, previous owner had the tranny rebuilt, and the people that did it broke a ton of vacuum lines and didnt put on a check valve, just put a rubber hose from the mod. to the metal vac. line.  The car shifted so hard at all times..  Replacing the modulator and check valve (make sure its on right!) should fix it, it sure made a world of a difference on mine.

The thing is, I HAD a check valve on there originally, they removed it and directly routed the throttle line to the modulator, and for a short time it shifted better...why would that be?