halogen bulb problem (87 jimmy full-size)

my brother hooked my truck up with some 90/100w halogen bulbs but the 90w when on low beams is dimmer then stock incandescent bulbs, i tried another set from him that were 55/60w and the same thing the 55 were dimm but the 60w were very bright. what is going on why are 60w with high beam engaged brighter then 90w low beam?

:banghead:

Poor ground at the headlamp socket. Follow the wire to where it grounds on the radiator support, clean the connection or replace as necessary. Look for green fuzz or rust growing on the connections or for a broken wire.