as Tim says, you've likely fried the fuel gauge by using 12V on it without a dropping resistor, although it could possibly have a bad connection to the sender which could have saved it, you can check the sender circuit with an ohmmeter - if you find an open circuit, determine if it's the wire or the sender that's open, and get a proper dropping resistor before you hook things back up
if the original style mechanical temp gauge still has the sender tube attached and in place in the engine, it's dead and not repairable by we common folk
and don't assume the speedo problem is the trans gear [driving or driven gear], it's more likely to be the cable or the speedo itself ... disconnect the cable from the unit, drive the truck and feel if the cable is turning, if it does the problem is a gummed up or broken speedo head - if it doesn't turn pull the trans end and try turning the inner part with a drill motor - worth pulling the inner part out and cleaning it well regardless
Bill
