Sounds like its overcharging, which can lead to electrical fires and such if you leave it at full charge for some time. but it shouldn't have anything to do with the fuel sender, unless its somehow effecting the gauge wiring.
Check and make sure you have all good grounds, battery to block, battery to body, and i would probably replace the voltage regulator and make sure it is grounded well to the body. From there you can see if its still doing it. If so, I'd clean all the connections at the bulkhead connections, alternator and the voltage regulator. If that doesnt do it, replace the alternator. But do not run it for long while it pegs the amp gauge.
as far as the sender, thats pretty odd that it works so funny. Make sure it has a good ground, the factory grounded it with a small ground strap attached to the hard fuel line.
