Hey All,
I've got an 06 supercab 4x4 with the 5.4.I bought the truck used with 75000 on it.Whenever it shifts into od at normal acceleration,probably about 2700 rpm's and 40 -45 mph it drops rpms suddenly to about 1500 rpms. It doesn't slip or anything it just drops drastically. Is this just converter lock-up or something else?
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That's normal, it's just your torque converter clutch locking in, to get better fuel economy.

 

yep, normal

the transmission WILL NOT shift into O/D until you hit 40 mph. my truck does it all the time...and it drives me bonkers when I'm in a 40 mph speed zone