I wish you would have posted this 3 years ago because it would have saved me lots of money. As my initial post stated on the Lexus Club Forum, I had 2 of the 3 problems you describe-- no mph reading and blacked out mileage. The mileage is not being counted when the cluster malfunctions for those who are unsure about that issue. I did send my cluster to Tannin and it was repaired at around $300 if i recall correctly. The 3rd problem of erratic shifting occurred when I purchased a cluster from the Lexus Club forum from someone who said they had a 1997 SC300 cluster. I found out that was not the correct cluster after installing it and my RPM gauge was redlining at 90 MPH. Because I only have the 1 vehicle I could not park the car. l considered removing the cluster while driving but read in the Lexus Club forum that starting the car without a cluster results in the airbag light engaging and having to have it reset by the dealership. After I got my cluster back I noticed the erratic shifting problem you mention as the 3rd issue so I believed my transmission was failing and I took it to a transmission repair shop. Somewhere in the Lexus Club Forum i saw a post that a failing solenoid is the likely problem. The repair shop claimed to have tested the tranny and confirmed thru testing that it was a failed solenoid. I paid for a solenoid kit and the cost to replace the solenoid -- around $600 with parts and labor. I still feel like there is still erratic shifting 3 years later. I did not believe the solenoid replacement resolved the problem so i will look at the part you describe and see if replacement fixes the shifting issue.
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hope it works out for you. but keep in mind, the erratic shifting i had would only happen if both the speedometer and odometer stopped working. Usually it would happen after my car sat out in the sun on a hot day for a lengthy period. if your shifting is erratic while your speedometer and odometer is working properly, then replacing the ceramic resonator may not work. But if all 3 symptoms are happening simultaneously, i'm confident it should work for you. Good luck!