GCP, Good for you making smart pick on last of the 5. 9's.
'06's & '07's are culmination of an excellent engineering run.
Tho' some, for good solid reasons, prefer early 3rd gen 305/555's, '06's & '07's have the fullest electronics pkg for both engine and transmission control, especially for towing and exhaust brake, best handling, best brakes.
Best early upgrade is FRANZ oil filtration bypass system to remove carbon/soot from oil. There's other oil bypass systems besides FRANZ.
Learn to use this website SEARCH function. FRANZ Bypass and/or Black oil re oil bypass filtration issues.
There's more information in the ARCHIVES than what most any person has time to read and most all of it's pretty good.
Also if you don't know for sure when transmission oil & filter was last changed, maybe never, then that's a good service to do, also well described in the archives.
Many in the know recomend avoiding transmission shop flush machines as do I since they can introduce lots of crud from their flushing unit.
Get the maint. CD.
www.techauthority.com. CD# 81-370-07059CD. $120. Best money you'll ever spend on your truck.
About a year or more ago some kind soul put up a free link for that CD and a BUNCH of members (I don't know just who... ,) claimed to have downloaded it for free before that link got removed.
Even spending the money, it's well worth it.
Performance upgrades take way way deeper pockets than what you'd initially think.
Don't worry honey, I'll pull it out just before... ,