I have a 2000 GMC Sierra 5.3l vortec engine shortbox. I have headers in it and a cold air intake. Its a 5 speed manual transmission. What else can I do like what kinda camshaft kit should I put in it. At 5 gear im doing 100 kms at 1500 rpms.

 

Don't go too far with a camshaft, unless you race. The lopping at idle will get to you. And extra horsepower doesn't come for free so expect to use more fuel.

A mild cam will not change your road-speed. Your transmission and axle ratio's do that. If you want better advice use this link:

https://www.summitracing.com/search/brand/summit-racing