Voltmeter trying to tell me something?

96 Silverado 305 When I replaced the battery about 5 months ago I noticed that the voltmeter was reading higher than it did with the old battery. I figgered that the plates in the battery needed some reforming and it would get back to normal. Over a few months the reading did come back down to a "normal" of just under 14v. Recently I have noticed it slowly bouncing around quite a bit. It has not had a problem starting so I am assuming that the battery is getting charged. What is going on here? Do I have a flaky diode in the alternator?

Thanx Mike