1999 Chevy Suburban Alternator noy cherging?

I have a 1999 Suburban 4X4 that the dash gauge for the charging system show half wat between the 9 and the 14. I checked the voltage at the battery with the car running and it said 14.1 volts DC. If I turn on all the accessories the needle shows in the red and I get a chek gauges light on the dash. I then checked the battery voltage and got a 14.0. Could there be something wrong with the alternator is could this be a gauge problem? Thanks in advance