Which mod first?
I'd go with the synthetic oil change first as soon as possibal , after reading a chapter in a mechanics text book years ago , about what happens in a new engine , shavings from all the parts working together , every new vehicle I've ever bought , I do the first oil change before 1000 miles and the second at 3000 . Go with an air filter system first . I use only K&N but thats my choice . You WILL see a nice performance gain and better MPGs , plus you will hear it working which you most likely won't once you put on a good exhaust system . I'd go with Borla , Magna-Flow , or Gibson STAINLESS , it's worth the extra $s to know you'll NEVER have buy another system for that truck . Then do the tuner . Each of the above mods done in stages to both of my trucks showed nice gains in both perf. and MPGs . 99 2-dr. Tahoe 5.7 , 20 MPG in the burbs , 25 MPG on interstates 2001 HD 2500 crew cab 6.0 , 16MPG burbs , 19 MPG interstate . And they'll both run like muscle cars when I want .