I had my truck in the shop to get the door fixed. While it was there the battery died due to not being able to shut the door. The mechanic charged it for me and it started fine however when I was in drive or reverse and not giving it gas, it would die. It would restart fine. I also noticed that while in gear and no gas applied the battery gauge would drop. While in neutral or park it idled fine. Today and at a stop sign it died and would not restart. It would turn over but as soon as it caught it died. It started right up with a jump but once the cables where removed it ran for a second or two and died. Took the battery and alternator in and both tested good. What could it be?
Most likely the battery is bad. And odds are the battery is beyond 4 years old anyway. Once a battery is run completely flat it is difficult to get it live much longer. Also jump starting a battery also causes more damage internally. I recommend replacing the battery first. And yes, I saw that the test said it was good. I have seen many batteries test good that really are not. Usually if the alternator is faulty, the battery (not charging) light will illuminate on the dash display.