vw sharan autotransmition problem?

I have a 1.9 tdi vw sharan 2001 the auto gearbox has started to behave very erracticly, it wont pull off in the correct gear and does not change gears. 1 and 2 gear and reverse it changes correctly but when I want to change from 2 in to 3 gear,I need to go to 7.000rpm to force to change, but after couple seconds its goes back to 2 gear again.This is hapens when I drive and I change gears on tiptronic with hands from - to + .But when I change the gears directly with autotransmission also I need to go to 7.000rpm to force to change from 2 in to 3 gear but after couple seconds its goes in to empty(blank).And when I start to drive the engine need to work a couple minutes and after that the gearbox may to start to change the gears but with the same problems which i wrote before.Please tell me what to do.