2002 Chevy Trailblazer Exhaust Leak vs. Lifter Knocking

I have what appears to be either an exhaust leak or a lifter knocking. I had our mechanic at my plant listen to it and he believes it is an exhaust leak because as the truck warms up, the ticking sound gets quieter. How hard is it to change an exhaust manifold gasket on this vehicle since that would be the cheapest route to try first and what steps does this entail.

Also the cruise control on this vehicle will not engage. Checked all the fuses and they are good. Would this be the switch or is there something else that could be wrong.