It really depends on the length and size of the mustang intake runners compared to the runners on the truck. My guess would be that the runners on the ranger are considerably longer than the mustang. If the runners are shorter than the trucks then they would improve the top end at the cost of low end.
Also, are the cams the same on the mustang and a ranger? If the cams are different, an intake with shorter runners on the ranger will not do you that much good without cams designed to take advantage of the shorter runners.