Transmission problems......

in Dodge
so I have a 2001 dodge Dakota that all of a sudden decided not to shift into 2nd gear until 4300 rpm....and so my husband being a mechanic looked at it and pulled the relay out from under the hood and went and drove the truck and then it was fine it only had 2nd and 3rd gear......can someone tell me whats going on? I took it to a transmission shop and they don't know either.
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