1997 sts runs warm purge valve other ideas

Just got this 1997 sts with the northstar. it runs 2 marks past center on highway. stting in idol it will stay at center, run on the highway for a few minutes it gets up 2 marks. the water pump, radiator, t-stat, hases, and recovery tank has all ben changed by previous owner, he got mad and sold it to me I knew this giong into it. I have read about her dreaded head problems, and also a purge line and ideas to start at ? thanks wayne

Check out this recent discussion. The Northstar runs hotter than most conventional V8's:
 
http://www.cadillacforum.com/m_12400/tm.htm