i have just purchased an 99 sts after the car is warmed up and hot it is hard to restart have to spin over at least 6 times before it will fire i have noticed when it is just half warm according to the gauge it is easier to crank it is as if it is not gettin any fire does not to seem to be a fuel problem crank or cam sensor maybe??

Have it scanned.
Crank sensors are common problems.

Fuel pressure regulator leaking down is another, but more so after sitting for a while( 15- 30 minutes)

Yep the most likely culprit would be the crank sensor. I would also suggest that another thing to inspect would be the distributor (http://www.partstrain.com/ShopByDepartment/Distributor) itself.

No distributor on a Northstar.

regarding hard start. my 1999 sts had the same problem. after replacing fuel regulator the problem was resolved. fuel regulator cost about $40.00, was easy to replace with basic tools, its found under cosmetic cover on top of intake manifold