To test your Fuel-temp-oil pressure gauge, hook 12 volts to the limiter and ground the case. Hook the output to the gauge to test. Hook a 10 ohm resistor to the othe gauge leg, then hook it to ground. It should go up to the Full - High - Hot line without going past it. bend the needle a little to set it.
The Clock and tach can be rebuilt with RT-Eng kits, not too hard to do.
I've gone with 3 different speedometers and they all seem to break because I put so many miles on my challenger. After the 3rd one's odometer gears and needle broke off, I think that I will go aftermaker GPS or electronic-mechanical speedo and put it behind the stock gauge face.
If you can't do this stuff yourself, you can always send it to Gregg here:
http://rt-eng.com/mediawiki/index.php/RTE_ClusterRecondition