1990 GT HB - Handling Issues ??????

OK, will give you a little background and then would like some thoughts from some of the suspension experts. I bought my '90 and it was almost completely stock. Noticed some bad tramlining (follows cracks in the road) and checked for wear. Noticed bad outer wheel bearings and replaced them. This fixed the following of the cracks, but did not solve the problem I am still having. The car handles great on smooth surfaces and bumpy roads. I have no problems throwing it around turns on back country roads and it feels tight when going down 5 lane roads on straight aways. It feels great on the expressway as long as the lanes are flat. My issue is when I am on the expressway that has developed crowing in the lanes from the weight of the semi's. Where I live, a large portion of the expressways have low spots in every lane where the constant weight of the semi's tire compact the roadway surface and leaves a high spot in the middle of each lane. These imperfections in the road cause my steering to be abrupt and makes the car wander constantly. It gets really bad changing lanes going from low to high and back to low. I checked wheel bearings, ball joints, tie rod ends, control arm bushings, and the steering column for play, and noticed a very slight movement in the ball joints. I replaced them with Moogs, rechecked the contorl arm bushings, and figured, since i was in there, replaced the front springs with 1.5" lowering springs as I hate the stance of the factory cars with the nose up look. This made the feel a little better on smooth ground when coming back to center, but did nothing to fix the crown in the road effect. I did some reading and found an article about lowering the front end, and that they recomended a little more toe in, so I brought the toe in by about 1/10 based on the the thread pitch of the tie rod ends. This still had no affect on the problem. I drive the car and feel for any play in the steering wheel and I cant feel any. I will tell you that when the tires hook into the crown of the road, it does want to move the steering wheel with it, and will cause the steering wheel to pull in my hands. I know lowering the car in the front may cause some bumpsteer, but I was experiencing this before, which is what prompted the new ball joints. Did the 1990 Gt's have issues with bumpsteer in stock configuration which is what needs to be addressed. I am stumped.