Rebuilt 454 running bad

Hey guys!

My uncle and I finally got the 454 back in the dually. He went to crank it up to warm the engine, and it would die after 5ish minutes of idling. He thought it was the alternator was not working, but when I put my meter on the battery, voltage when the motor was running was 13.5 volts, so it isn't the alternator. When I was testing his theory about the bad alternator, I revved it up to about 1500 rpm, and it ran nice, but when I let off the accelerator, it tried to idle, but couldn't keep a steady idle speed and died. Now it won't idle for anything :| . Anyone have any ideas as to what's going on? I'm thinking it may be the IAC (idle air controller, or something like that), but he keeps asking me if that was the problem, why isn't it throwing a code. As far as I know, the IAC isn't electronic, is it? Also, the motor is throwing a P1345 code, which is CKP and CMP sensor correlation code. From what my grandfather is saying, there is a learn process for that that has to be performed while driving. Both of the offending sensors were changed before putting the motor back in the truck. Any merit to what my grandfather said? We would drive it and attempt the relarn procedure, except that my uncle didn't put the torque converter back in in preparation to drop the tranny to get it rebuilt. Any fresh ideas are always appreciated. Thanks guys!