This has been discussed previously, It improves with mileage and only affects some CT's, My brother and I bought CT's at the same time and it affects his and not mine. I think some of the fault is when taking off from 1st the tendency is to click up hard and fast for the first few gears and then tail off when 60mph is reached, by the time its suitable to select 6th say on a big straight road, you tend to select 6th more leisurely and here the problem arises. Try and select 6th as you would 2nd or 3rd and let us know if it improves