Which tire are you running? I have the Kendra Klever RT and it’s at 34.76” diameter. Was curious to see how far I’d be off from you. Did you change the 726-15-01 and 726-15-02 and then relearn PCM/TCM? Thanks for the info.
I also idle sometimes as long as you do and it does shudder. I think it’s just the engine design. My wife’s Expedition does it as well in the school line. Her’s is 2 years older but same engine and same shudder at idle.