Car seems to constantly "wander" at 60+ mph.

it could be a bad spot in one of the new tires, or wheel alignment was off slightly

I think it might be your intermediate steering column. There is a u joint on the steering post that can corrode and seize causing a boaty type feel on your steering wheel at higher speeds. I replaced pitman arm, idler arm, ball joints and tie rods both inner& outer before we realized the culprit was the steering column u joint. I found one at a salvage yard in perfect shape for 25$. Lincoln wants $263 for the part. Just be sure the u joint moves in all directions if u can find a used one. It should take a good mechanic about two hrs to install. Good luck.