98 sts idle stall, have done alot of research on here and still need help please!

Hello all, I've been lurking and researching for a while but my stubborn butt is out of options and need you guys' help!

First off I'm a backyard mechanic who was ase cert. a few years back when I worked at a shop so I'm decently well versed in this stuff but this one's above me. I've got a 98 sts with 209,000 miles. I bought it with 190,000 on it for $200 with blown head gaskets. After researching my options on here I decided to go with the suregrip studs and have had no problems whatsoever there- what a great product! My buddy and I pulled the motor out the top (for all you naysayers who say it cant be done that way) and we had it done in 2 weekends, went pretty smooth. But anyway, my problem now is the infamous stall at idle after the car is warmed up. Does it about half the time at stop signs/lights, and it will do it when you slow down for a turn sometimes. It will also stall in park after it is warmed up, also rather randomly. The car accelerates and cruises very smooth, just the slightly rough idle and annoying stall. The only code it ever sets is P1599, stall or near stall detected-that's helpful

After reading on here I have pulled and cleaned the t.b. and iac, checked my fpr and my fuel pressure(42 at idle, 46 with vacuum line pulled of fpr) checked my maf and intake hose(clean, no cracks or tears in hose). I understand from reading on here that the ckp's on mine are not the bad mexican one's and if they were failing they would throw a code, correct? I have not pulled and cleaned the egr, also figuring that would throw a code if were malfunctioning enough to cause the stall? I don't think it is ignition related because of the lack of a missfire code. I have checked repeatadly for a vacuum leak and have found none. I am about ready to take the car to a shop, which goes against everthing I believe in as a car guy I am tired of the wife complaining about it and wanting a new car, so please, please give me any and all opinions and ideas!

Thanks in advance for you help,
Ben