Captain Obvious Alert - I'd say the answer lie in whatever is suppose to trigger the relay.
How about the "in park" switch? Anti-theft key failed?
If you set the emergency brake and put the truck in gear, will it start if you hot wire it?
Have you checked for any codes?
A bump if nothing else!
- Mine: '09 GMC Sierra LTX ECSB 2WD - Deletes, 4" Exhaust, AEM CAI, DP LMM 2.6 Stg 1.5 Drag Turbo, BD Manifold, Diamond Eye Downpipe, All Season Diesel Performance EGR/Grid Heater delete, PPE Race Valve, Edge Insight, '08 Hummer Wheels, DSP5 - EFI Live tuning by Mark Broviak @ Danville Performance.