Lack of power transit twin wheel pick up 90psi 350t?

This truck I know has had an axle change from 5.13 to 4.63 so that should make the vehicle pull better, but it doesn't. I have cleaned the egr out, no difference. On a flat road it will go up to56 to 57 and sit at 2,500 revs. Gutless on hills. This vehicle has been fitted with a low ratio diff and chipped. The vehicle has done 135000 miles. I know it has had a new pump and was fitted at Carlisle ford. It is a 52 reg. Can anyone help?