How to remedy when a previous owner has not maintained a vehicle....

I have a 2003 Cadillac Escalade With 140K miles.  I purchased it almost 2
years ago with over 117k miles.  Recently we have had the starter,
alternator, and battery replaced after it just died while my wife was driving
with the kids.  In the time we have owned it, the shocks and part air ride
suspension has been replaced.  It seems like the previous owners did not
keep up on the maintenance since the 100k maintenance was not done
when we bought it.  Also, I think that it sat for a while prior to us buying it.  
Is there anything that we can do to make up for the poor maintenance and
time sitting?  I use it to pull a pop-up camper and it tows great.  I want to
know what I can do to keep it going.....  Any help would be appreciated.