1. Speedo is mechanical, not electric
2. Fuel gauge is dependent upon the signal from the fuel level sender...that is likely corroded, common problem after all these years
3. If the temp gauge is rising quickly, you could also have an issue with the temp sensor or blown head gasket
4. The tach...check your ignition coil connections

It will behoove you to look up and download the factory service manual (FSM) from mitsubishilinks.com and review the troubleshooting portions.

If all else fails with the FSM review and you determine that you do indeed have a defective gauge cluster, look me up. I have a few clusters for sale.

Cheers,
Russell