The "problem" with new vehicles is that the factory engineers are pretty smart,
and have already done the easy stuff.  20-30 years ago, it was pretty easy to make
dramatic improvements in vehicle performance with a few simple changes.  Not so anymore.
   The improved air intake/filter is a good first step.  The factory doesn't do this
because they also have to meet noise restrictions.  You may have noticed that your
new air intake is noisier than stock.
    The throttle body spacer is probably a waste of money.  Try removing it and see
if you notice the difference.
    Reprogramming the computer should be your next step.  That really is the best
bang for the buck.   I used Hypertech, but I've heard a lot of good things about Jet
as well.  Do this before doing anything else.
    Headers will make almost no improvement below about 4,000 rpm's.  The factory
exhaust is quite good.  Personally, I wouldn't do it.  Lots of expense, pain in the
behind, and very little improvement.  Same with a cat back system.  Sounds better,
but no power increase to speak of.
    If you want better pick up and towing capacity, consider changing your rear gear
ratio.
    As for the factory warranty, refer to the Moss-Magnusen warranty act.
Essentially, it says that if you make changes, you are responsible for those changes.
 But if something else fails, the warranty is still valid.  For example, if you add
headers and cat back exhaust (emissions legal), and you break a valve spring and
trash the motor, the warranty is still in effect for that trauma.  The entire act is
available on line.

I also forgot to mention that I put the Flowmaster series 40
muffler/dual exhaust (single in, dual out) on my truck as well.

The power gain for a K&N in more a state of mind than anything.The
little flow increase is obtained with less filtration as is well
documented in some ISO test on line.  Modern engines are well tuned on
intake and exhaust from day one and if power gain where if fact that
easy, they would come that way. On the headers, you will loose low end
torque and responce and MPG in town too. If you want a real boost that
you can feel in the seat of your pants, regear the trucks axle one
step deeper. You lack displacement to make any serious torque but
deeper gears can bring it to life and let you better use the power you
have and contray to popular belif it will not hurt MPG with OD tranny
and city MPG will likely improve because you will get off of power
wasting stall of torque converter sooner.
-----------------
The SnoMan
www.thesnoman.com

As far as the warranty goes:  If the modification causes a failure, then the
warranty does not cover it.  Dealerships can find ways to say that a
modification voids the warranty.  Especially with an aftermarket computer
chip.  If you want my opnion, I would leave the truck alone;  and buy an old
beater truck to rebuild and modify.  You will have no warranty worries.
There will be more parts available, and for a cheaper price.  If your truck
is your daily driver, then you won't have to worry about be stranded or
running out of time.  Another thing is that older vehicles can for the most
part be more simple to modify.  The thing I don't like about modern
vehicles, is that it seems I can't fit my hands into some places.  Sometimes
to get to things, you have to take apart too many things to get to what you
are fixing/modifying.

Yes, sell it and get a diesel