I already answered your question on LS1Tech.com.
How are you having trouble finding a PCM from a 5.3 truck? Check www.car-part.com or Allen can probably hook you up with one.
I'd name other places but don't want to step on any toes here.
New Truck on it's way: '07 Classic GMC 2500HD DuraMax LBZ
03' Silverado ECSB 4x4 Z71 LQ9, TR230, Patriot LS6, 31lbs, Trailblazer stall, Corvette servo, Corsa Touring,
HP Tuners
SOLD - 99' Silverado ECSB 4x4 5.3, Edelbrock RPM, Nitto Terra Grapplers, Texas-Speed Tuned 02' PCM, LT1 fans