Here's what I did with mine:

I took mine off the car, and opened the front "plate".
Under that plate, you can see a coil spring that presses up against a plunger that deals with the vacuum line on top.
I cranked up the tension with a pair of plyers with one hand, and tightened the nut with a wrench with the other hand.
That really cut down the range of vacuum from (I'm guessing) around 0 - 5.
It shifted harsh, clunked into first, the whole bit.

I then loosened up the nut again, and the spring wound out a little. That opened up the range of vacuum, and the eliminated clunking downshift.

So, what does this mean to you? Probably nothing. You might need to get a new one. You can get one for approx. $50 every now and then on Ebay.

I would still take it off the car and see if I couldn't fix any obvious problems with it, though.