I have been dealing with similar issues with our Freightliner M2112 since we took delivery of this rig as a new build. 5 sets of steers in 270,000 miles and countless alignments, sets of shocks etc. I think we finally fixed it, but it's only been a month, so I am holding my breath. As you did, alignments were done, rear axle was never out. We, too, just recently had 14,000 lb springs installed, because the 12k ones were curving backward due to 13,300 on the axle when no cargo was onboard. The handling improvement was tremendously better. Next, new front wheel bearings and races. Next, a mechanic noticed that the Accuride rims had measurable runout, meaning they were bent, wobbling side to side as they rotated. These have a 5 year warranty and we got replacements. I ordered and had installed with the new rims a set of Tru-balance wheel centering devices. When the mechanic had the rims off, I was amazed how much movement the brake drum can do, it's like the holes are 3/8 inch larger than the bolts. Then after all this, new Bridgestone tires to replace the Goodyears. It was very hard to find a size that is a true Over the Road, long haul type. We had always had what turned out to be Regional service tires. An important difference, we learned. Probably have 8-10 thousand miles on the new set up and we have run as fast as 73 mph for hours in Nebraska and there is no sign of improper tire wear and absolutely no hopping or vibration. Still have a bit of pull to the right, so will try the two different tire pressures fix suggested. Hope some of this helps.