Hey guys I have a problem. When my car hits approximately 90mph it shakes violently. Now I have a 02 GT with a tubular k member and a arms. It's always done this since I swapped out the 3.8l that used to reside in it, but I'm wondering why? The 4.6 SOHC from an 00 GT is just bolt ons, but my suspension Includes a PA racing k member and a arms, steeda comp springs, mm subframe connectors, tokico shocks/strus, and mm cc plates.The alignment is good, tires are balanced (245/45/17s), but at 85-90mph the shake is really bad? Ideas as to what's causing this? I do have my stock a arms and will be putting them back in with steeda x2 balljoints and bump steer kit, not that I think those two parts are the major issue, but perhaps the a arms? I also post on mustang evolution and posted there and they said to have my car road force tested? Anything else/ideas you guys can think of? Please help if you can and or have had this issue before.