leeboy

About a week ago, i started up in the morning, and after it ran for 30 seconds, my check gauges light came on. I looked and the charging gauge was slowly creeping up to midway. Once it got to midway, the light went off. Now when i start it every time, its like it takes a little bit of time befoe the gauge moves and the light goes off. Sometimes, the light goes off , when the gauge is half way up, then the light comes back on and finally goes up when the gauge reaches midway. After the truck is warmed up , and driving, the gauge sits at about a fraction over the midway point. Any ideas?