max voltage output on a alternator at 2800 rpms

Defective alternator - internal voltage regulator.

Voltage output should not fluctuate much. It should also never be 17 volts! What you check at higher engine speeds is amperage output. Consider this: the voltage in your electrical system should be such that all your electrical accessories and processors function, while recharging the battery. 13.7 - 14.2 maybe is a good range. 13.4 is too low. Your amperage output should be 100 amps peak -- so, figure you'll see about 75-85 amps at 2,000 RPM. If you've replaced the alternator, first you must check to verify the new one is functioning! Not all replacement alternators function out of the box. Second, check very closely the wiring connector to the alternator. This connector can be damaged and melted, causing electrical issues and the concerns you speak of. Good luck!