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2001 F150 Crew Cab 4x4. 5" Skyjacker and 3"body lift. 35" Kumho MT's. 5.4L and automatic tranny.
Truck runs fine. Accelerates fine. No shake or shimmy or anything. However, when I reach cruising speed and the transmission shifts into overdrive the truck starts shuddering. Let off the gas and the truck coasts smooth. Give it gas and shift into lower gear and higher rpm and no shuddering. Only in overdrive when rpm drops to about 1500 or less does shuddering take place. Just bought the truck so I don't really know the history. Has approx 112000 miles. When this issue started I also noticed that where normally my truck idled steadily, now the idle was a little erratic. Not bad but not completely smooth. Just noticed that my check engine light does not work so I am going to get some codes read and see if there is anything there. Also have oil filter, transmission filter, fuel filter, and spark plugs to change in case that might help.
If the transmission oil is original, the addatives can wear out. There is a known problem called "converter shudder" which is a vibration on the transmission area due to worn out transmission oil. Change the oil with MERCON V and the filter and see if that helps. Your 2001 should have a drain plug on the torque converter also. Bar the motor over with BIG screw driver on fllywheel teeth untill you see something like a 1/8 inch pipe plug size plug in the converter. Drain out 8 quarts on teh converter and take 5 out of the trans oil pan.