At lower speeds 45 -55 it surges like searching for a gear. Fine at higher speeds in overdrive, but when I am going up a big hill and it needs to drop a gear to keep up the speed it surges and seems to search for a gear. Anyone seen this issue and can advise? Thanks

 

The 4R70w isn't my area, but do you mean it hunts between third and fourth, seems like neutral, or slips?

How many miles are on the truck, and when was the last fluid flush?

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Adrianspeeder