Slightly Embarrassing Question

what tires are you running, i just put a set on a 2008 dodge pickup and got to having a real bad vibration, i though it was a tire out of round,got to reading the sidewall markings, even thought they were radials they were made of nylon, and everybody from the 70s remember how they got flat spots when they sat, after driving about 40 mile the flat spots would start rounding out. I thought they had done away with nylon tires, but i assure they haven't, had mine put on in dec,2017, already took them off and sold them and went to polyester to get rid of the vibration...just a thought