I have a 1997 XLT, 4 door. I changed my Firestone Wilderness AT tire, after 59K miles, with Pirelli A/S Scorpion from size 235 to 255, 70 to 75, R15. It looks great !. But I'm encountering a problem: The driving is not smooth. I can feel vibration of the steering wheel at 65 mph speed. I came back to the tire people (WTC) and they rebalanced all the wheels but the same thing! I also noticed that the lead weights that they put into the rim is big and two pieces on the other rims, unlike before, it was only oneweight and small in size. What is wrong? Help