you misinterpreted Rick, a plug in battery charger will change the 'rate of charge' depending on how "smart" it is [amps, not volts] - an auto regulator should deliver a steady voltage that may vary slightly with RPM, with the amount of current sent to the battery depending on battery condition - sounds like yours is doing the job now
notice your ammeter right after you start the truck, when cranking it should show a discharge [indicating current is flowing out of the battery], as soon as started the meter should show some amount of charge, indicating the regulator is sending some or all of the amps produced by the generator to the battery, and that rate of charge will taper off as the battery returns to fully charged, so the meter will return to 'neutral'
Bill