Need more traction on 03 Cobra

To get right to the point: I have an 03 Cobra and it seems like the rear wheels spin so easy that there's no point making any more power mods - not like I've made a lot already. I have a 2.93 pulley to install but don't want to till I can hook up better. Rolling in the slow lane doing 40 mph, dropped into 2nd to pass the guy in front of me, and as I swung out to pass, the rear end started fishtailing all over the place. And one more thing - I know, grow up - but I want to hear some good tire sqeal like my 97 Cobra did. This one just sounds like a belt sander when the rears break loose. OK guys, what do you think?

Thanks U.M.

I just put 18" rims with 285/35-18 Pirelli P-Zero Rosso Assimetrico's on the back, 220-AA-A. Could not go bigger because the rear rims are 9.5" wide but was hoping the better tire would make up for not being a 295 or 315. Haven't really had a chance to try them out yet because it's February, I noticed for some reason a lot more tire spin in cold weather.

I was thinking about next maybe stiffer shocks or a Motoblue hard launch cross bar, any opnions on these or is something else maybe a better next step?

http://www.rpmoutlet.com/03cobraharda.htm

Thanks.