Just this morning, my battery light on my dash started flickering while driving. It seems to stay solid when I am at a stop, then flickering when I accelerate.

I took it to two different shops and had them check the battery and the alternator, and both shops said it looked fine. I did put a new belt on this weekend, so my belt shouldn't be loose. Also, when I start the truck in park, and when it is in neutral and reverse, the battery light stays off, but the second I put it into Drive, the light comes on.

Any ideas what could be causing it?

 

Verify the charge indicator light is functioning correctly (key off/key on). Next pull the 3 wire plug from the alternator and check the condition of the terminals (if your alternator has a separate single wire connector with a white/black wire, check it as well). If they look good check the voltage on the yellow/white wire (should be the same as battery voltage).