A video clip may help (reasonable sound quality is important); one of the engine whilst being revved stationary (gently bring the revs up, let return to idle, then floor accelerator) and then one of the rev counter while driving (max acceleration in second gear, and keep foot on the floor, don't change up).
Worth checking earths; the main one on the inlet manifold (back rhs of head)- loosen off and re-tighten. Also the small brown wire by the ECU, and the ECU mounting nuts too; again, loosen off slightly and re-tighten.
Other possibilities include restriction in the exhaust, due to either disintegrating cat or collapsed silencer, or obstruction in the airbox, such as a plastic bag (had this on a diesel, and took ages to find!).