Voltage too high...

Regulator is what controls the voltage.

Are you sure the alternator/regulator is wired correctly? I suppose it could be a problem with the alternator itself (ignoring control signal from regulator).

Also, verify that your meter is OK. There's alot of AC "Ripple" in the charging circuit which could be throwing off your meter.
 
Dude I had the same problem. You could hear the fuel pump wig out. I tried multiple regulators, different alts, nothing worked. I ended up getting a GM internally regulated alt with a lifetime warranty from autozone.108 amp, easy bolt in. Just open the mounting hole to the head a little and bolt it in, wire up a BATT, and ign wire.
 
If the field line going to the alternator gets a full 12 volt signal, it will cause the alternator to overcharge.

I've done this purposely before using a jumper wire to test my regulator.

Check for a short between the field and the Batt terminal on the alternator.

The difference between regulators come with the higher amperage and then having a digital or mechanical. I run a 100 amp Ford alternator and matching digital regulator out of a mid 80's E-350 ambulance package. It's a nice unit.
 
Same problem here, 17v at the battery, and it was a short at the alternator harness. The harness that plugged into the alternator was bent too far and I guess was causing some pins/wires at the connector to short out. After a new regulator at $35 I finally fixed it by wiggling the connector then bending it at a less severe angle.