our ford automatic transmission with overdrive keeps going in and out while driv

our ford automatic transmission with overdrive keeps going in and out while driving down the road any idea whats wrong with the transmission thank you

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What year, model and size engine is in the truck? What speed or speeds does it go in and out at?
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replying to Doug , boots wrote:

2000 ford f350 dually 7.3 diesel between 50 n 70 mph
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