I have done everything. 3 sets of tires, 5 alignments, and it still drifts right. I did use monroe struts on the front and by-passed with resistors. Not sure if that could be it. Also installed new springs all 4. Can't figure it out. I'm also thinking of buying new stock OEM struts for the right price. I need the 580-462, both sides.
What's the history on this car? Has it been in wreck? Have you tried different alignment shops in those 5 times? No other steering or suspension failures found? Really, 3 sets of tires?! Doesn't sound right.
Try this & it won't cost you anything, but it might not solve your problem. Go someplace where you can drive your vehicle in a circle full lock for about 10 times one way, then another 10 times full lock the other way, with no acceleration or vey little.
Sounds like something is wrong - or grossly worn - with toe-in or tie rod ends.
The original AC Delco F55 Magnetic Ride Control struts for the OPs 2003 STS are pretty inexpensive in Rock Auto - about $562.00 apiece. GMPartsGiant has them for $637 apiece. GM list is over $1100 each.