Got a P04 code coming up, which is ECM communication fault. Unit cranks but wont fire. Swapped ECM out and truck ran fine. Fitted new ECM.

2 weeks later same code and fault came up, ECM faulty again, tested on another unit. Anyone came across an issue like this? Seems like a wiring issue or a shorted module/sensor may be blowing the ECM, but then again I thought it would have blown a fuse before it blew the ECM. Don't want to put another ECM without locating the cause. Not really sure where to go next other than pulling the whole harness apart.