In my case, I personally think this truck was struck by lighting. Went to a trans shop. Sat for 8 months. Went to get truck in shop to do trans and they couldn't get it running.
Kinda glad this thread popped up, mine is doing the same thing and I still can't track it down. Only code I have is p1694 and it just cranks. I tried good used ECM and that didn't work. And I saw post above about truck sitting for a while.. Mine has been. This all happened when going from a raptor to a FASS
Just an idea but I chase down a chased down a similar issue, thought it was ECM, gave me a no start issue, asd relay was going crazy, and had no bus on the dash... Long story short turned out to be a fuse that was getting a crappy connection inside the fuse block... The block is two pieces and tends to separate