Swaying issue help

Hey guys back again...i have a 99 gp gt coupe. 140000 miles, new sumitomo tires, gmpp sway bars front and rear, new slotted drilled rotors and ceramic pads, ngk ix plugs, msd wires. I noticed on my way to work this am that my rear end is wanting to sway. Not too noticeable on smooth roads but throw some bumps on at 60 mph and wow its like playing grand turismo on expert!!! The rear feels like it just wants to kick out and can really complicate driving. It seems the car is driving me not the other way around. I know i need new struts but have been saving to get the lowering coils at the same time. I did the sway bar kit which helped but nowhere near solved the problem. The car is in amazingly great shape but i dont know where to start. I've only had it for a couple months so im still getting to know it. Any advice on this issue would be greatly appreciated.:confused:

To start it doesn't help improving the handling when you have worn out steering or suspension components. If those are the original struts at 140K miles then the struts should be replaced. Also, was a 4 point wheel alignment ever performed? Best to do that after new struts which IMO should help resolve your issue or help detect worn out components.

Thanks BNaylor...much appreciated as always. Like i said i have only had the car for a short time so im unsure if the struts are factory or not. I do know that i havent had a 4 point alignment though. Judging by the ride quality i would have to guess yes they are the originals. So you believe the correct course of action would be to replace my struts, coils, and mounts and then do the alignment and see where im at? Any opinions on the 1" drop coils?

Thanks again:)

Dropped coils usually throw off the suspension alignment points (especially caster/camber), and put undue stress on other suspension components such as ball joints and strut mounts. I would suggest against them.

ok...thanks richtazz. I was wondering what to do because i really would like that look but dont want to do any harm to any of my other components.

The biggest issue and complaint with using aftermarket lowered coil springs is side effects such as the "pogo" effect. Camber can be brought in within factory specs with a camber kit you add to the strut. So it depends on what brand lowered coil springs and struts you decide to use. For example Eibach kits with KYB struts are a bad combination. Best one to use is the GMPP kit with either Koni or KYB AGX adjustable struts. The GMPP kit lowers it by approximately .75". Also, you have to be careful with wheel/tire sizes 18" and above within lowered coil springs. Regardless there will be the cost consideration versus the end effect and results. Nice to get rid of that gap you see between the tire and fender or have it lowered but is it really worth it. I really don't see much to be gained in handling or adversely affecting the ride.