i cant figure gimp out for crap. what do i use to drop, remove rear bumper and roof racks, and change the tails?
I don't know the specific tools in GIMP, but I'll tell you how I'd do it in Photoshop. Should be similar.
Use the eraser to get rid of the bumper and roof racks.
Find a picture of the tails you want. Use whatever select tool you choose to grab only the tails, copy, switch back to your truck, paste, then move and resize to fit.
To drop, select the entire truck except the wheels, then use the move tool to bring it down. (TIP: Holding the shift key while moving in PS allows whatever you're moving to stay in line.)