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Mark, you are getting good advice from Danny and Gordon, both here and in the links they provide. The Mark Harney articles Danny links to are the generally accepted Old Testament on Weber setup and tuning.
But there is a quick-and-dirty test you might try before pulling everything apart, especially since you say the car was running well before you moved.
I live close to sea level, at the foot of the Sierra Nevada mountains, and my carbs are tuned for that, but most of the good Speedster roads around here are up in the foothills, so I drive at higher elevations a lot. Up to about 4000', there's no noticeable performance hit. By 5000', there Is, and up at Lake Tahoe - 6000' - the engine is definitely down on power, and the idle has dropped noticeably.
If I'm staying up at Tahoe for more than a day or so, I'll do a quick tweak on the 'idle mixture' screws to raise the idle back up and help low end response. As a test, you could do the same to see if that makes any difference. It's possible your jets and idle circuits are clean, and you just need a slight retune. If so, the engine should respond to this little test.
Try backing off (unscrewing) the 'mixture' screws about a half-turn. Do each one the same amount and note how much you turn them so you can set them back to where they were if this makes things worse. The screws are marked 'idle jet adjustment' in the photo Carlos posted above. They're knurled, spring-loaded thumbscrews, made to be adjusted by hand.
It's probably a good idea to do a complete teardown, cleaning, tune, and possibly a rejetting, as Danny suggests, but this might make the car more drivable for now.
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