My 7.4L has a 4 speed auto trans, it drops down from 4th to 3rd.
It will drop down to 3rd after about 10-15 minutes running down the freeway, from any speed. It will not upshift back to 4th. If you pull over & turn off engine for a few minutes, it will shift normally until it down shifts again to 3rd.
I had the transmission rebuilt & it still does it. HELP !
Have you checked the throttle position sensor ?
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