the programmer is well worth the money it is very easy to use, you can
change lots of settings, i use to own a 02 4.8 single cab swb i had
flowmaster exhaust, i had k &n intake FIPK II, 3.73 rear end, hypertech
programmer. all of those things helped but when i added the programmer and
used premium fuel i really noticed i difference. your really not going to
get an extra 55 hp by little performance parts the only way you would get
that much would be to get a supercharger like a said, i now own a 06 sierra
w/ a 5.3 and it is plenty fast, what do you need 350 for it will allready
beat a hemi, and the ford 5.4, i know from experience

Hypertech has dyno charts for basically everything....this one is the same
as yours (and mine for that matter).
http://www.hypertech.com/get_dynochart.php?cid=70&vid=1423886&tp=pdf

On paper it doesn't look like a huge amount, but the feel is way more than
that. I set it back and forth from no program, regular and premium several
times over a few days. The premium fuel with reprogrammed shift points is
the best, but premium is $$$. The regular fuel option with shift reprogram
is the best all around for me, You can also used it to change the
transmission shift points seperately from the performance program. You can
read stored trouble codes with the programmer as well. Well worth the $350.
Oh yeah, if you have an OnStar vehicle make sure you REALLY read the manual
thoroughly.