Jimm 1/20/2013The PCMs may be interchangeable to a point - depending on the year, the engine size and specific transmission. The PCM will still need to be reflashed / reset-up by the dealership to be correct for the vehicle it's installed into - and calibrated to the specific vehicle components. The PCMs are VIN protected so unless you flash it you cannot go from one vehicle to another. There is another consideration - the security code - some vehicles have the security code in the PCM, and some do not. Those PCMs with secuirty code will not easily interchange with a PCM without.
By the way, the 4.7 is different from the 3.9 and 5.x series engines and the PCMs are not interchangeable.
As far as the no BUS condition - you may have a loose/bad connection. Check the plugs and pins for corrosion, and inspect the wire harness between the PCM and the dashboard for any worn insulation/bare wire/frayed wire or anything else out of the ordinary.