I'm sorry you got this far, and so frustrated. Your first post was Saturday night, and it's fall... people are doing stuff. LOL, you're so frustrated I almost hate to post this!
The temperature gauge and fuel gauge only have one thing in common, the 12V supply voltage. So, if any other gauge DOES work, then it's possible, but unlikely your issue is in the gauge cluster, because other gauges using the same 12V source work fine, I gather.
I think you just might have a bad fuel sender and a bad temp gauge. I'm going to address these separately:
Fuel Gauge - The fuel gauge reads a sending unit in the tank. The sender is a simple variable resistor, with one end grounded. The resistance spec is 22.4 Ohms empty, 145 Ohms full. So, you can use the ohm function of a common digital test meter to verify the sender. The wire from the sender to the gauge is yellow with a white stripe. You can get to it at two places. The first is near the tank, the pigtail from the fuel pump. The second place is a circular connector with 8 positions under the hood, just under the master cylinder.
For the pigtail at the tank, disconnect the connector and figure out which end goes to the tank. Then use your meter to measure resistance from the white/yellow wire to ground, which is the black/yellow wire. Do this with the ignition off. It should give you somewhere between 22 and 145 ohms, like I mentioned before. If you do this right, and get a solid measurement outside that range, that is the definitive test for the sender and you will have to replace the pump/sender unit. Doing the resistance test at the tank takes about 15 minutes if you have and understand a voltmeter and resistance measurement.
If your resistance is in range and makes sense compared to how full you think the tank is, then go on to the connector under the hood and do the same thing, except that you won't have a ground in that connector, you will have to find some bare metal for the ground. The wire to measure is, again, yellow/white, and again, engine off, please. If memory serves, you want to measure the male side of the connector, but don't count on my memory. If you don't get a value on one side of the connector, test the other side! You should get a value similar to the measurement at the tank. If not, then you have a wiring issue from the tank to the engine bay. If that's the case, we can get into how that harness is routed.
Temperature Gauge - This is somewhat similar. 74 Ohms cold, about 10 Ohms hot. The sender for that is near the thermostat housing, the sender has a single pin connection. Now, just for future reference, there are actually two temp senders, one for the gauge, the other for the engine computer. The engine computer sender has two wires and a plastic connector. Measure resistance from the sender pin to ground for the sender at the thermostat and see if that makes sense in the range I mentioned.
Both of these senders have a significant history of failure. You can do all of these tests in 30 minutes or less. I would rule out the senders before going any further with the gauge cluster. But, since you apparently have the gauge cluster out now... you might consider two unrelated things. First, I highly recommend you replace all the illumination lights in the cluster. This is cheap, easy and you will be staring right at them, so why not. I mean, they are 25 year old light bulbs.
Second... if you are not aware of the oil pressure gauge/switch issue, the oil pressure gauge is not an actual gauge. It uses an oil pressure switch and if there is oil pressure, it moves the gauge needle to a certain position. You can make this work like an actual gauge though. To do it, you need replace the sender switch with a common analog oil pressure sender. That's easy, you get to it from underneath, it's towards the front drivers side. But you also have to do a modification at the gauge cluster, you have to bypass a 20 ohm resistor. Here's a thread on the oil gauge:
How to: Make Oil pressure gauge perform like "real" gauge
If the sensors are ok, then we can talk about the wiring in the gauge cluster itself. I have helped about a dozen people with the fuel gauge. Only one of them ended up with a problem at the gauge cluster.
Finally, there is a factory manual with wiring diagrams and test procedures for the various switches and systems. This is the EVTM manual and they are all over Ebay for less than $20. Get one of these... you will not regret it.
I try to check this forum daily, usually early morning. But, this being fall, and me being in northern MN, I am busy getting ready for winter, including a pretty major repair job on another truck. But, ask your questions and I will do my best to help.