Hey guys, sounds like there's several problem being brought up here, I'll try to help best I can.
On the 99-02 trucks the odometer/PRND123 display will go out intermittently and come back on if you hit a bump or bang on it with your hand - this is caused by a poor solder connection where the plug is soldered to the circuit board and it can be repaired. See here for a guide on how to do it - Silverado odometer problems
The fuel gauge problem on that generation of truck us normally caused by a bad fuel sending unit on the fuel pump assembly in the tank, requires replacement.
On the 03-06 trucks the gauge problems are typically caused by bad gauge motors which can also be fixed, here's some info on how to fix them yourself - Silverado instrument cluster problems
That generation of truck also has fuel sending unit failure a lot which will cause the fuel gauge to read wrong, requires replacement.
The 03-06 trucks have another issue where the entire instrument cluster will quit all at once and sometimes come back on/off/on, chimes ringing, lights flashing,etc. This can be caused by a faulty ignition switch, requires switch replacement.
And finally, on the 03-06 trucks if you notice the 4 gauges on the right quit suddenly all at once along with lights coming/staying on it's a failing IC chip on the circuit board - cluster replacement required.
Hope that sheds some light and can help some of ya.
Oh ya, one more I see a lot - if your oil pressure gauge is bouncing from 0psi to 80psi don't panic, it's not your motor or your gauge whacking out. It's a poor electrical connection around the oil pressure sensor/switch causing it to read full pressure then 0 pressure.