Your temp gauge sensor is in the cylinder head drivers side rear with a one purple wire plug. You can ground the plug and if ther gauge pegs it is the sending unit. Real easy fix and usually at NAPA <$15.
The fuel gauges are notorious for errant reading you can clean up the connections on the power strip in the gauge cluster and at the tank if it is dropped. Other than that get used to the odometer trip set for when to buy fuel.
I had problems with my gauges and replaced them all with inexpensive Sunpro units. I would have replied earlier but I just installed the sending unit for the fuel gauge and so far it works fine. If I had a newer jeep or deeper pockets I would have chosen Auto Meter or something similar. I can send pics and details if you are interested.
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