Vu transmission problem help?

[sunshine the vu]

Hey every one so for a while now my vu Ute v6 has been playing up so when im at the llights if I take off full accelaration "flooring it" when it goes to change gears my rpm goes up and down frantically causing the car to jolt and the only way to stop it is to take off the accelarator and then reapply its done about 229 thousand kms and just recently had a transmission service what could be causing this?

I will even try to get a video up tomorrow sometime to show my problem thanks any advice much appreciated