dsg gearbox help,main dealers baffled!!

Hi all here's my problem,ive got a 2007 Passat dsg saloon SEL -
when the car is cold it drives perfectly,changing sweetly through all gears.After 10-15 mins or so when warm it judders quite violently on acceleration until it hits the speed you desire then its smooth if kept at desired speed,if you need to accelerate,it then does the juddering thing.It happens accelerating from any speed,but as ive said it doesn't happen at all when cold.
Ive had into dealers they have "supposedly" upgraded to latest software and changed gear oil and filter,they gave me the car back and said all fixed,i was overjoyed and drove away from dealers feeling elated,all for about 10 mins,when it started to do exactly the same.http://www.passatworld.com/smilies/sad.gif
I took it back and left it with them,i called in a week later to see if they were any closer to fixing it at which there reply was "we dont know what the problem is,there are no faults stored in system,we will have to change the gearbox at £stupid money.I wanted a second opinion so i paid them £££ for the gear change,diagnostic and oil and filter change and took it to some local "VAG specialists" they too didnt have a clue other than to change gear oil first then if not fixed,change box.
Has anyone out there had this problem,or know what it will be,
thank you in advance for any replies