Why is my tahoe alternator only putting out 12 volts i have had it tested 3 times and they say its fine... I have a new battery but wen i use to much stuff it drains my battery help me?

If your alternator is working, and your battery is not recharging, you may have a cable fault. Check your connections from the alternator to the battery positive terminal. Sometimes corroded wire is the culprit. Too much current is being used in the path to the battery. You want that current at the battery.