Update: Shimmy Problem solved
Steering wheel shimmy 65-75 mph from day one on my 2014 overland with 20" Fortera tires. I test drive 4 new summits and they all did it. I purchased my jeep 1 1/2 hour from home to get a good price. My first attempt was to bring it to my local dealer who road forced the two front tire only. It still had the shimmy but not as bad. The dealer told me he could not help me any further. I started a case file with chrysler and took it to a different dealer. The mechanic stated he found a slight vibration caused by the stones in the asphalt. Then I took the service manager for a ride and he stated they all do it and the 20" tires are worst. He also stated it is caused by the electric steering assist, but he road forced all 4 tires with the hunter 9700 machine. He stated the road force came in at 9, 12, 10 and 5 pounds. When I drove it home the vibration through the vehicle was better but the steering wheel shimmy was worst. I called chrysler the day after only to find out the dealer had closed the case stating it was the nature of the vehicle. I re-opened the case with chrysler and took it to the dealer where I purchased the Jeep. After 4 hours the shimmy was finally gone. The dealer stated one wheel had a road force of 36# and got it down to 24, another wheel was at 26 and got it down to 17 and the other 2 wheels came in at 8 and 12 pounds, and two of the wheel were off balance by .75 oz . He put the 8 & 12# road force tires in the front and the 24 & 26# in the rear. I drove the vehicle home with no shimmy at all. Upon reaching 75mph I felt a vibration throughout the seat. I stopped by the goodyear store and they replaced the two rear tires and got the road force at 5 and 9 pounds and my grand cherokee drives smooth as silk up to 90 mph. To make a long story short, it is the tires, they just have to be road forced balanced on a good calibrated machine and if they can't get the tires under 12# then get a new tire. By the way goodyear paid for the 2 rear tires after I called them and got a case number. I had a shimmy and vibration for 2,200 miles. My front rotors were also replaced at 725 miles due to steering wheel shimmy when the brakes were applied at 45 mph. After 7 weeks of hating my jeep I now love it!!!