Chevrolet Repair: 2001 Chevrolet Express 3500 Cuts Out - Wont Restart, chevy express 3500, crank sensor

Question
My partner and I did a engine swap for a customer,in a 2001 Chevy Express 3500 extended passenger van, with a 5.7L V8. We test drove the van for about 60 miles over a 2 day period, and had no issues at all. Customer came to get the vehicle, took it for a simple test drive, then turned it off. It then would not restart, showed a MIL giving the code P0101. We cleared the code, and it immediately started, but died on the customer within 2 miles of the shop. We then replaced MAS, and it seemed fine again. Again the customer doesn't get to leave our parking lot before another MIL, it abruptly died, and would not restart. We again scanned for codes, and we've gotten several random codes; P0101, P0107, P0300, and P1345. We again reset the distributor, we used our snap-on scanner to dial in the timing, and we are getting a P0101, that kills the engine abruptly, and won't allow a restart until the code is cleared. Ocassionally it will throw in P0300, and it's the same thing. We used the snap-on scanner to reset everything we can think of, and still no change. We are unable to drive the vehicle 1 block; it cuts off without warning, or any particular situation. We changed the crank sensor also; still no change. We have picked the brain of every tech we know, and still are at a loss. Any ideas?

Answer
HI DAVID,OK I GET WHAT IS GOING ON.LET ME CK MY DATA ON MY ED AND I WILL GET BACK IN TOUCH WITH YOU WHEN I HAVE SOME INFO ON THIS..GIVE ME THE BETTER PORTION OF THE DAY...TOM

HI AGAIN DAVID,WELL I SPENT SOMETIME ON OUR WEB SITE [IATN]THIS IS A PAID SITE FOR TECHS AROUND THE COUNTRY THAT YOU CAN ASK IF THEY HAVE RUN INTO ANY STRANGE PROBLEMS. HAVE YOU HEARD OF IT ??? IT IS A GREAT SIDE...NO RESULTS ON THIS..THIS IS A PROBLEM I WOULD LIKE TO TACKLE IF I COULD GET MY HANDS ON THIS I LOVE STUFF LIKE THIS....BUT I WILL THROW MY 2 CENTS IN IF YOU WANT ME TO..THIS TO ME SOUNDS LIKE A CLASSIC CASE OF LOSS COMMUNICATION PROBLEM BETWEEN THE PCM AND SENSORS..THE REASON I AM SAYING THIS IS BECAUSE OF ALL OF THE ERRONEOUS TROUBLE CODES..PO300 RANDOM MISFIRE AND PO101 MASS AIR FLOW PERF AND ON AND ON THESE CODES WOULD NOT SET FOR WHAT THIS VAN IS DOING IF ALL WERE GOOD IN ITS WORLD..SO MY FEELING IS AND YOU SOUND LIKE A SMART GUY, BUT HAVE YOU CHECKED AND RECHECKED ALL OF THE GROUND WIRES AND CABLES ON THIS ??? [VERY IMPORTANT] WE HAD A SIMILAR PROBLEM THAT DROVE US NUTS..BEING THOUGH THAT YOU JUST REPLACED THIS ENG AND THE PROBLEM WAS NOT THERE BEFORE  [I AM GUESSING]I WOULD BE LOOKING AT WHAT I SAID AND ALL CONNECTIONS AGAIN JUST TO BE SURE.CK FOR ANY PICHED WIRE THAT MAYBE SHORTING OUT,GRAB HOLD OF THE WIRE HARNESS AND GIVE IT THE SHAKE TEST..DO YOU HAVE A GM TECH 2 SCAN TOOL BY CHANCE ?? IF YOU DO, YOU COULD TRY TO FLASH THE PCM  AND SEE IF IT WILL LET YOU..JUST A THOUGHT. IF BY CHANCE YOU FIND WHAT IS WRONG WITH THIS AND IAM SURE YOU WILL,, LET ME KNOW AND GOOD LUCK TO YOU,,,TOM..