Why is does my car rev once it hits 2 on rpm's? on 2000 Volkswagen Jetta

Your drivin my car (TDI Jetta auto) and once hits 2 on rpm's than revs out all way till you let go of the speed. But sometimes doesnt do it and it shifts gears so nicely. so stupid. Any idea's ?

Asked by for the 2000 Volkswagen Jetta