jsieao

I've read the numerous threads on this symptom. I don't seem to get the shudder at highway speeds. I just drove to Florida from WNY without an issue. The only time I notice a shudder, is trying to maintain a low speed for any distance. My daily commute takes me through a school zone that requires a 20mph limit down from a 30mph limit. While trying to "feather" the gas to maintain that 20mph speed, the shudder is horrible. In a few of threads I read, someone mentions changing the driving mode for these situations. That seems to work for me, but making the other driver of the truck understand this isn't going too well......
Anyways, I was wondering if having tires that are a different size than original effects the program for transmission shifts.
The tires I have are a bit taller than the originals, so I'm actually moving about 4mph faster than the speedo is depicting.

djfllmn

iTrader: (1)

how many miles and original plugs?

jsieao

Just under 60, but less than 6K after cam phaser repair

16IngotFX4

Yes, larger tires will affect transmission shift points.
Your tires are going to be quite large if they are 4mph off at 20 or 30 mph. Tire size percent different is the same as a speed. For example, if you install a tire 3% larger, all speeds are off by 3%, so 3% of 30 and 3% of 80. It's only off by '4 mph' at one given speed.
Instead of changing the shift mode I'd just lock out a gear, drive in 3rd gear on that road. The motor is probably just lugging. Assuming you have a 6-speed is why I suggest 3rd. Pic a gear where 20 mph is cruising along at 1500 minimum.
I just vote for locking out the gear and if the 'other driver' finds that to be silly, just let it be and when you drive, do as you please.

When we had 4-speed transmissions I would drive in 2nd gear pretty much every day to leave a neighborhood. It keep the RPM up and helped with warmup times. My F150 has by far the worst shift strategy of any vehicle I've ever owned (but I haven't own very many) and before this I was in a 2008 vehicle.