We just bought a new house and i have a truck with a 6" lift and it wont fit in the garage.I need 2 - 3" more.Can u cut 2-3" from the header?

absolutly not... code only allows you to drill holes or "cut-outs" for pipe or wireing.. This is a situation where you unfortunately will have to literally raise the whole header which means a new door etc.. please do not simply cut it to size as the integrity of the header will be lost and you'll get sagging then eventual breakage.. then you've a whole new can of worms to deal with..

That header has been sized to be able to hold up whatever is above it, roof, second floor, whatever.
But in most cases if there's room above the header to move it up it can be raised to the next sized higher over head door. But it's not really a DIY first time job. Done wrong and down comes the house.
Something will have to support all the weight while it's being lifted so a temperary wall needs to be built, the siding and sheathing will have to come off, cripple studs cut, new shorter jack studs get cut to fill in the space between the header and the old jacks. Then all the old trim around the garage door opening gets redone.(if it's a brick home I'd forget about changing the height).