I always keep and eye on the voltage meter, and I usually check it while cruising downt he highway. Within the last few months, it has been dropping a few tenths of a volt every time I check it. It used to run right around 15.6v (off of the guage) with everything electrical on (including my amp) and now, it has dropped to a constant 14.3v. It doesnt seem to matter what I leave on electrically, or temperature, or engine rpm either.
The battery was new back in January, and still reads 12.0v across it.
So im wondering is my alt. going bad after 9 years & 110k, or is 14.3v still acceptable?

14.3 is quite normal. Mine varies from mid 14's to mid 13's depending on load. A/C seems to be the biggest draw. I wouldn't worry about it.

I agree with Ranger. Start worrying when it is charging in the 12s with no accessories on.

I have a '97 Aurora in which the DIC reads 15V + when charging. The strange thing is that also the oil pressure "sometimes" reads abnormally high. I wonder if the calibration may be off on these readings.

It probably is off. Check it with a digital volt meter, and I bet you'll be around 14.5V.