I'm curious to see any informed responses you get here because I think I've got this same issue. I get an intermittent shake or wobble that resembles an out-of-balance wheel at certain speeds in my truck, too, and during a recent garage visit the mechanic told me my steering rack needed to be replaced because there was play in it.
I told him not to touch it and have been driving it for about two months now since he said that, and other than the occasional wobble I honestly don't notice anything that would otherwise indicate my steering rack is shot. I found a video showing how to replace the bushings in the steering rack, however the video was filmed using a 3rd gen and I'm not sure the same service applies to the 4th gen. If it does, I'm definitely going to try that route first before dumping well over $1,000 into replacing a part that shouldn't be work out yet in the first place.