I have an 03 Alfa See Ya on a Freightliner chassis. The tires were weather checked after 10 years and 60,000 miles. Plenty of tread left but they made me nervous. I replaced them with a set of Hanc...
I would have gone with "all position" tires. I do not know where your "tire guy" was coming from. There is also some that are considered "all season" especially for the NW. I would say that it is possible that there is not enough air in the front tires. Have you weighed your rig? If yes, then check the tire manufacturer's website for correct inflation. Does your rig have a steering stabilizer? This should slow down some raod wander.