First of all......
Knowing that the vehicle is still local to you is a huuge advantage, it narrows your search from a needle in a haystack to a needle in a bale of hay. Here are some ideas:
Post up some pictures here on our website.
Carry pictures of the truck with you and hit all the local car shows / cruise ins and talk to Chevy truck owners about your search, maybe even have some copies of the pictures to hand out that say "Cash Reward - have you seen this truck".
Get one of those custom t-shirt places to make a t-shirt up that says "Cash Reward - have you seen this truck" and have the picture put on the t-shirt. Where the t-shirt at the car shows and around town at events, parades, etc.
Become a local cop and run the plate yourself. 