yes it works when i turn the key forward but gos off when i start the truck

How long has it been acting up? Could you have gotten some bad gas?

about a month but if the gas was bad it should run bad a the start up to because at start up it sound like a champ nuttin but as soon as i put it n drive are turn on ac while in park it run bad and voltage meter drop to 6 volts then comes back up in about 30 secounds.

i changed my plugs and wires but still the same problem i notice when i give it a lot of gas it dont cut off while in drive i was thinking something is sticking so i pulled off my alternator and brought it to auto zone the guy said it pass but it was turning very slow so do u think it could just be the alternator turning to slow when n drive .

i changed my alternator and still the same problem help please????????????????????????

how many miles on the truck? when was the last time you changed your fuel filter?

truck has 108000 miles and i changed fuel filter last week end

ok today i put a meter on battery before start up its 12 volts after start up its 15 volts so then i left truck in park and ran the ac truck voltage drop and started to kill on me any1 want to add there in put

im still waiting on some more input

May sound silly but have you checked all your ground points on the truck.