Rezon, going to radial tires on my truck was one of the best upgrades I've made. I replaced nearly new but old 16" bias ply tires with 215-85-16 radials and the "follow ridge" issue all but disappeared. Many of my local roads I suspect are similar to your roads (I rented a vehicle and drove many miles in Italy last fall).
On the steering sector, sure sounds like it has internal issues. First step would be to check and add the proper grease if necessary. There are many post on this site that are applicable.
One thread is here.Recient thread that mentions a rebuild kit with part numbers.
Buona fortuna
RonR
