Hi, I need some help. I bought a 2011 Ford f150 with a 6 inch lift kit. I have 35X12.5X20 tires. When I bought it and headed down the road, the speedometer was about 5 to 6 mph off. I called the dealer, took back in.

Took out and still 5 to 6 mph off. Dealer said they put PCM on and put at highest setting. Now dealer wont even return my phone calls.

Took to another dealer, the tech said, according to the PCM, it wasn't set at the highest setting. So this tech said they maxed it out, should be only about 1 mph off at 70.

Well you guessed it, I took it out and is still 5 to 6 mph off. I called the dealer, they said it is my GPS that is off. I checked my speedometer with watch and mile makers at 60 mph, my GPS is right on.

Do these dealers know what they are doing or am I stuck with a speedometer that cannot be recalibrated???