first of all take second and fill out your signature, so we can all know what your drive, and be more helpful with mods in the future. the 3K GSK kit will allow your engine to defuel at a higher rpm, more closer to 3K rpm, than say 26-2700 rpm, the 4K kit does the same, but goes even further, and you need to install valve spring in order to keep the valves from floating with a 4K kit, you dont really need them in a 3K kit, but just watch your rpms, especially if you have a manual truck, dont try and rev over 3200RPM without valve springs. i would reccomemd them for a mild setup, you will definately like they way youe engine revs, and pulls after they are installed. hope this helps.
wes