I have a 2000 Mitsubishi Galant with a 3.0 V6. When you accelerate hard, the steering wheel shakes. I assumed it was the half shafts, so I had them replaced with no luck. The rotors have also been replaced and the tires are ok. Does anyone know what else it could be?

Well are the tires balanced? But it could very well be a bad suspension or steering component , or a bad engine mount. I would think that it could be most likelly bad outer or inner tierods on one or both sides of teh vehicle. Mostly teh wheel with the most TQ on acceleration. As yu are accelerating the wheel is moving in and out in small incraments back and forth causing the steering wheel to shake. Lift up the front of teh car and with teh tires on , grab the front side and rear side of both tires and gentlly attempt to move it in and outnot in big movements short quick ones and see if there is any play.