Vibration when pulling hard tipronic Gearbox

Hi guys new to the forum dont know if this is where i should put this thread.
The situation is that my vw ag5 flx tiptronic gearbox vibrates the whole car under heavy acceleration on the 3rd gear when it reaches just over 3000 to 4000revs then it changes to 4th gear.Is this normal on a diesel tdi 115hp,on all other situations everything seems ok.
planning to have filter an atf oil changed now that it has 86000klm on the clock.
Will it be wise to put a litre of LUBEGARD atf protectant when i have the atf oil changed.
Tks in advance for any advice and keep up this great and very complete forum going.
Best regards
Joe Guilherme