[davester3500]

gmt900 trucks I don't believe you can swap bcm's like you could with gmt800's, they are more vin locked.

I would suggest :
-get codes for what is happening for the ecm
-make sure the security system is happy (there should be a chip in the ignition key, which the security module reads, and communicates w the ecm to allow starting)
-work through the no-start diagnostic procedure on charm .li for your truck.

 

[davester3500]

Diagnostic procedure for that code:

U0140 — 2007 Chevrolet Silverado 2500 4WD V8-6.0L Service Manual | Operation CHARM

Detailed repair manual for the 2007 Chevrolet Silverado 2500 4WD V8-6.0L.

charm.li