fuel gauge is most likely the sending unit, bust out the trusty multimeter and shop manual
speedometer could be build-up causing the cable to catch. try taking the gauge out and shooting some lube down the cable. i dont know about classic guages, but my old blazer had a magnetic spinning thing on the back that would sometimes catch and cause the needle to dance, varying with speed.
Speedo "dancing" is generally the speedo cable binding in the speedo cable housing. Remove the cable, clean it and re-install with fresh GRAPHIE lubricant.
WD-40 is NOT a lubricant; it is a SOLVENT! (That's a whole different topic)
Test the fuel gauge by grounding the sender wire at the tank. The gauge should now peg at FULL. If is does, the gauge is OK; if it doesn't, suspect the sender or the wiring. Simple.
Speedo "dancing" is generally the speedo cable binding in the speedo cable housing. Remove the cable, clean it and re-install with fresh GRAPHIE lubricant.
WD-40 is NOT a lubricant; it is a SOLVENT! (That's a whole different topic)
Test the fuel gauge by grounding the sender wire at the tank. The gauge should now peg at FULL. If is does, the gauge is OK; if it doesn't, suspect the sender or the wiring. Simple.