1st off if you lowered your car your stuts are NOT the problem. Most likely you will need to buy an aftermarket Cast and Camber kit...this is why your shop could not get your alignment done correctly, because they could not properly adjust your toe and camber because you dont have Cast & Camber plates.
Buy some C/C plates and THEN take it for an alignment. This should fix your tire wear problem.
I had the same problem on my GT when i lowered my car, even WITH my aftermarket struts AND cast & Camber plates. I took my car to SEARS to align and they couldn't do it right and my tires wore bad.
So i took my car to my shop at my technical school and did the alignment myself and adjusted the toe and camber with the Cast and Camber plates, and i put it as close to factory spec as i could, and my alignment is great now. Stupid freaking SEARS....
Keep in mind:
If you do decide to spend your money on the C/C plates and an alignment, you will STILL need to buy aftermarket struts soon. As the lowering springs WILL wear on your suspension more now, and will rapidly kill the life of your struts.
I recommend getting some C/C plates and aftermarket struts from
www.mustangtuning.com Its a great site, and if you enter STANGNET as a coupon code at the end of your order you get an additional 5% off your order... plus most of their stuff includes free shipping!