vectra 1998 loss of power at 4500 rpm s???

[paultintin]

hi, i have a vauxhall vectra 2.0ls 1998 (r reg) iv only had the car a few months but ive noticed that if you put your foot down to pass another car the car gets to 4500rpm fine then its as if the rev limiter comes on and theres a huge loss of power if i step off the gas or change up the car carrys on pulling fine. recently changed plugs,oil & air filter and plugs but its still the same could it be a dodgy sensor or something.