Battery/ALT/electrical

My Battery light has been coming on when I drive my car for about a mile or two and then goes off, until today it just stayed on. I ordered a belt tensioner thinking it is slipping a little bit and/or my ALT is going bad But still check 13.8 volts from the Alt at the Battery not the back of the Alt. So I had to get a new battery tonight since I have been running on it for days but now my O/D light just started blinking on and off and my E-brake light has been coming on when I excel or stop quickly for months and I just thought it was a sensor going bad or loose, But now I wonder if I have a bigger electronical issue? Could this be two seperate issues all together? Or is there electronical problems that I am over looking?

Thank-You very much for listening!

Jeff B in Pittsburgh PA