I cant tell you if there is a problem causing the tranny to search other than the speed you drive is the sweet spot where its trying to lock up as saudade mentioned
but I can tell you if you want to save the trans then dont let it do that
if it does it for too long you will toast the trans
if its constantly searching then change your speed or shift down to 3rd
your mileage will go down on the trip but you will save your trans