First of all it has a 1 year old chevy 350 in it. I know its a chevy. But when I drive it will sputter and almost die, you have to put it in neutral and try to rev it a little bit. Like its running out of fuel. I thought it might be the fuel pump so i put a new fuel pump and filter on. Still no change. It will do this after a full day of wheeling and the engine is not over heating. First time it did it only 2 time. Yesterday it did it about 6 times. Now when it sputters and dies, the battery will have gone dead as well and wont start the truck. I have to get a jump to get it started, after a jump it will run for a while and then do it again. It will do it at any speed. when i check the out put of the alt it reads 14.2. The battery reads 12.3 but drops to 9.5 when I just turn on the elec cooling fan. Right now i have the battery on a charger to bring it back up to full. I have had the alt tested and it tested good but gave a diff out put reading each time. it has a q-jet carb on it that was rebuilt a year ago. The sputtering just started out of the blue one day. I have been wheeling it all summer up to this point with out any trouble.
Any ideas on what to check?

Have the battery load tested after charging.

Thats the next thing i'm going to do. The battery has been on charge for about 2 hr at 6amp and still shows at low on the charger.

do you have electronic ignition if so maybe coil pickup in dizzy . does it do once it been running or will it do it when it's dead cold also.

All the specs you listed, is that with the vehicle running? If so your not getting charging voltage to the battery. Which will cause loss of power to you HEI ignition system or external coil, docent really matter. Are your liights dimming out as well when running?
If you have charging voltage at the alt. But not the batt. There's a wiring issue.

or a fan that consumes a lot of amps and a bad battery that consumes the rest.

Sure you bet process of elimination.