1998 Nissan 240SX Nissan Skyline power surge

Engine Performance problem
1998 Nissan 240SX 6 cyl Two Wheel Drive Automatic

Hi there, firstly I should mention that I own a Nissan Skyline but there wasn't an option available in the drop down box. Not sure if that makes much difference in any case.

Anyway, I find that I tend to get a surge of power or acceleration somewhere between 90 - 95km/h which makes it hard to cruise on the (100km/h) motorway at a constant speed.

Would you be able to shed some light on this? I haven't encountered this problem in any of my previous cars and am not sure if it is a problem with the transmission, throttle, engine, etc. Thank you.