Esequiel

I have an 01 cummins 3500 6 speed and it will turn off after about 1 minute of starting it. The battery gauge is marking low, like 12 volts. Also the "wait to start" light won't come on sometimes and when that happens it won't start, I have to wait a few minutes and try again to get it to start but then shuts off again. I have a p0122 code for the apps. I replaced the alternator yesterday but had no luck with that. Batteries are ok and only about two years old. I replaced the ECM, cam sensor, and VP-44 about 3 months ago. ECM was programmed with the vin. The truck also runs with sputter at about 1700 rpm and at 220 rpm. The apps was replaced about a year ago by a certified mechanic. I tried to reset the apps but still didn't help. What is wrong?