Dave,

It really sounds like you're on the right track by checking vacuum AT the modulator. All that gadgetry on top of the valve cover that simulates the vacuum of a gas engine can be tricky.

Yes the modulator should hold a vacuum from your mity vac, or whatever you're using, forever. Also, I think the modulator might be adjustable by spacing with washers or something. Luckily, as I'm sure you already know, the modulator is cheap and easy to replace.

Oh yes, I remember now also, there is an orifice in the tee that comes off the main vacuum line that leads to the brake booster. If this orifice is not in place the trans won't shift correctly. It seems like I did some searching and found some info about this with some detailed info about that line and orifice. As I recall, my daughters car was doing the opposite though, it was shifting into higher gears way too early, so the orifice probably doesn't apply to your problem. I'm sorry I can't remember more about it.

If your vac measurement and modulator testing don't reveal a problem, you might rig up your mity vac to apply a measured vacuum directly to the modulator to see if it reacts as it should. That would tell you if the problem is with your vacuum gadgetry on the valve cover or the modulator on the tranny.

Oh yes, also don't overlook the vacuum module gadget on the back of the injection pump. There is linkage that hooks to that gadget from the linkage on the engine side of the IP.

I'm sorry I can't be of any more help. I passed the ASE test on automatic transmissions, but you may have noticed from some of my posts that I'm just a manual transmission sort of guy.

If none of this helps, keep posting or email me and we will continue to dig into this problem. It's gonna be a long drive in second gear to College Station for that Aggie girl if we don't get it fixed.

BTW, I'll bet you're staying nice and cool with your parallel flow condensor and 134.

Fly safe and good luck,