Scan Tool will be needed
Here is Chevrolet procedures:
Not sure of your experience, but that is GM instructions from manual for:2002 Chevy Truck Avalanche V8-8.1L
As you see the CKP is located in the rear of the engine, top at the Bellhousing mount of the Block.
This is not a job for unskilled.7 of 1 - 10 labor skill
Also, Updated Scan Tool will be needed to reprogram