My truck seems to have an alternator problem

My truck seems to have an alternator problem. When hot, the voltage will drop to 12.5 sometimes and stay there, then for no reason, jump back to 13.7-14. Engine revs or electrical load does not seem to matter. It has every electrical accessory available with a 160 amp alternator. The battery is relatively new also. The voltage drop is slow, not sudden, as is the rise. I have checked every connection I can find, to the point of checking terminal grip. I was an ASE Master tech before closing my shop a few years ago, and would have sold a customer an alternator already. I am on disability now, and $275.00 is a big chunk of money. Do you have any ideas of something I might have missed?