need your help again guys

every now and then whilst driving my gti 16v, it pulls back when the revs get quiet high. its like you hit 3 or 4000 rpm an it jerks until i take my foot off the accelerator. i dont think its the timing because the belt was changed about 2 years ago and never had a problem. my brother put it on his vagcom machine and it came up with check speed sensor or something like that, im wondering if its got something to do with that?? plz help