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Well, the common problem theory is out. The fuel guage had a cold solder joint, the tach had a bad tach module (the '86 module works in the '91 cluster, BTW), and the temp guage had a bad sender. I had the meter connected across various grounding points relative to the battery and everything seems to be OK. I also wedged a piece of plywood under the passenger side engine mount, which may have reduced the front-end shake even more. I will probably swap the mount (it looks bad) and shim it up perminently to see if that helps.