A complete tranny fluid exchange sound like what you need. Your mileage and now this shudder are two good reasons to do it. I did mine in the driveway and the shudder went away. Good luck.

 

Well, at 97k, if the plugs are original they are overdue.

 

Agreed

 

Hello,

I have a 2007 F150 that was doing the same thing. I just got it fixed. I had the plugs changed three weeks ago ($329) at the dealership. The problem came back. I took it back and the #7 Coil was weak. They replaced the coil and that one plug and the problem went away. I have 95,500 on the truck. I agree with the others that it's probably the plugs and/or a coil.

I still love this truck.

Good Luck on getting her fixed up!

Wayne