2000 Nissan Bluebird silphy 1.5 performance issues

[oanica]

Good day,

I drive a 2000 Nissan Bluebird silphy 1.5 petrol, and find it very nice and quiet, but after 60mph its very slow to respond and after 65mph it doesn't go further. I was suspecting the MAF but i changed it and no result, changed the spark plug and nothing, now I'm thinking about changing the fuel pump. just to be clear i tried a diagnosis and the computer says the car is OK.
I noticed a oil leak on the engine but i dont think this is causing the issue.Can you guys help me out?