My xtrail revs goes up when I hit over 60km/hr

I have a 2005 nissan xtrail nt30 with just over 200k km on the clock. It starts ok, idles ok and kicks back ok during gear shift. Revs remains ok (1500-2000rpm) when i drive from 0-60km/hr or maintain that speed. Problem starts when i go past 60km/hr speed, the rev goes up with speed! To get to 80km/hr even on downhill, the rev has to be 3500rpm. To get 100km/hr, the rev is 4000rpm and up it goes with higher speed . I maintain a gentle accelerator pressure for car to pick speed for itself and the engine does not whine during these high rev speeds, i even checked with a diagoniser if all the gears shifts and they do. I Changed transmission oil, changed transmission solenoids, changed spark plugs, checked the speed sensor. And all these have yielded no results. I checked the fuel pump and checked the fuel filter and it is ok. I even checked just to be sure that my clock is working ok... Did a full tank and drove on a highway at the high revs and the fuel was gazzled up. I am lost for what to check and i need help. The high revs are not economy friendly and driving at low speed is neither an option