05 INTL 4300

Truck shakes at speed 40-55 .i mean shaking kinda sideways.i dont feel much vibration on steering wheel,i do feel it when i hit the brakes.(have air brakes).just recently changed two new front tires,and recapped rear tires! mechanic suggested king pins,changed! then suggested a Ujoint,changed! then one of the front bearings,chaged! and shaking/vibration is still there!! now he says maybe differential! and another U joint!!kinda tired of it and the guessing game while it is costing me an arm and leg!!! any suggestion??