Transmission skip
 

on my 06 3.8 i have developed an occasional skip and grab in high gear around 1500rpm on gradual acceleration.... no codes are present ..shifts fine,strong thru entire range and only does this in high gear ( 4th i think ) it almost feels like an engine misfire it is so rapid... once above 1500rpm it clears up... shop but a chrysler approved additive in there that seemed to help somewhat but i would love to figure this out before it leaves me stranded somewhere... thanks for the input