Ah, another CA car guy!
Our cars do have a vacuum transducer that is supposed to calculate the proper amount of vacuum to go to the tranny. I know one of the things this is based on is boost, but I'm not well-versed on exactly how the transducer does its thing. The transducer is the blue plastic thing on your driver's side fender that sends a vacuum line down to the trans. modulator. It's pretty close to the fuse box.
That being said, your problem sounds like a vacuum leak somewhere and probably has nothing to do with the transducer. When I got my car it shifted very hard, too. I discovered the line to the modulator was not actually connected! You've probably checked that already but it took me a while to figure that out. In my case there was so much oily crud stuck in the unconnected line that all the vacuum in the system didn't leak out of it.
If you haven't tested for vac. before there's a great pictorial on
www.dieselgiant.com. However, be aware that since you have a CA car, your vac numbers will not necessarily match up with the ones shown on his pictorial. When my tranny is functioning properly I've discovered I have 22.5 inches hg going to the tranny at idle, and I think the regualar federal cars are supposed to have 15". 22.5" is the full amount my vac pump puts out.
The vacuum leak could be anywhere in the system. If you have any vacuum components that aren't working as well as they should be like your door locks or your vents, that would be a good place to start testing. It's also possible you have a leak in the modulator itself or in the rubber part that's also down there. You could test those things by taking the vac line off the transducer and using a vac pump to create a vacuum in the line going to the modulator. The modulator should hold vacuum; if it doesn't there's a leak down there somewhere and you've isolated the problem.
I've had a number of vacuum issues and I've already asked a lot of questions about them, so you might not have to. I would suggest doing a search on my user name and 'vac' or 'vacuum.' You might also search for ConnClark, he's another guy on here with a CA car. His info. has been valuable to me and might help you, too.
Sorry if you already knew most of this. Good luck!
Oh yeah, to see if your kickdown switch works, just floor the pedal when you're driving sometime. The car should downshift to give you more power. If not it may be need to be fixed but it shouldn't cause the hard shifting you describe.