hello i have a 306 r reg late 97 and the gears work fine when in 1st 2nd or 3rd when you put it in d and it changes gear fine when going through 1/2/3 when it goes in the 4th gear it revvs up really high to like 5000-5500 then changes any help? i was going to get the auto gearbox oil changed but there wont be much point if i need a new gearbox the car has only done 66000 miles any help would be great thanks.