I have a silverado 1500 2003 with a 5.3 and I was looking at some bully dog tuners and I like the ones with the monitor and the gauges that tell you what your engine is doing what are some good ones like this out there that are under 300 dollars
The stock gauges work pretty good... If you want to get the most out of it, you could just have the truck tuned (HP Tuners, EFI Live, etc). It makes a world of difference.