It is because your torque is falling. As a result your acceleration g's are also falling the higher you are in the rev range of each gear which means your rate of acceleration is less the higher you rev, compounded by losing torque multiplication in each higher gear.
Gearing will not make that feeling go away, it will just seem like you are going through the gears faster, and the car will be quicker, but the feeling of power falling off will remain because it is.
The only way to feel like it is pulling hard to redline is to tune it to make peak torque at redline, so you end up with flat torque across the rev range. You can do that with this car, but it will mean lowering torque down low to about 180wtq and keeping that flat to 6500. you would make the same peak of 220whp but with linear acceleration, reduced wheelspin issues, but would be slower if you were trying to go WOT at lower rpms.
the next way is a bigger turbo, that can make a higher level of torque at redline, and make the same flat curve so that horsepower (and as a result, acceleration g's) will climb in linear fashion to redline.