I changed out the electrical connector with the 2 "O" rings on my transmission because of a leak and the leak has stopped. The trans shifts smoothly under light acceleration but upshifts hard under heavier acceleration. I put a OBDII code reader on the car and no codes came up. I have read that replacing the valve spring in the trans corrects slippage between gears but I'm wondering if it also fixes the hard upshifts? Since there were no codes; I figured it probably isnt the electrical control plate under the valve body. Any suggestions?
Thanks
John

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1985 300TDT
2013 E350 Bluetec