cmayna,
I did exactly as you did and incorrectly diagnosed a bad gauge. However, the fuel gauge is probably the one gauge that it is worthwhile to have a spare of (its seems the most sensitive and most prone to failure/abuse, the most expensive to rebuild, and its price has gone up over the past few years). My trucks will be in the family for a while and I bet this spare will eventually prove useful.
As you probably found, poor grounding of the gauge and the sender and good connections are key factors in why fuel gauges do not work correctly (of course, freying a 6v gauge with 12v can cause failure).
Tim
