voltage drop while driving causing dead battery
 

I have a 2003 Silverado and for some reason my battery keeps dying on me. I will get a jump start and i can sit in nuetral and the battery will charge up, i can shut the truck off and start it again but as soon as i put it in drive the rpms drop and the truck kinda bogs down and the voltage meter is showing a drop to about 9. I can drive the truck for any distance i want but when coming to stops or turning its starts to bogg down and i get the voltage drop again, then if i shut it off after driving the battery is totally dead.

The battery is only about 4 months old so it should be holding a charge and i had the alternator tested and it tested good i was also thinking it may be a dirty throttle body but any other ideas would be greatly appreciated.

Figured out what it was i cleaned the throttle body but my 4 month old duralast red top had two bad cells good thing it has a 2yr warranty got a replacement for free.