Funny , how is the fuel truck going to affect the stair or loader if both of them are in position ?
It will surely will, depending on the airplane size, and the position of the fuel point.
While it's easier on a plane with a big wingspan to have a fuel point placed in a spot where the fuel truck won't crash into the positioned stairs, it's almost impossible on a smaller plane so, if the stairs are moved back on the starting position at the parking, they will never crash with the fuel truck, unless the parking size totally wrong for the airplane size (but it will probably get a "too small" parking warning from GSX anyway).
But again, this is an issue only with planes with the refuel point on the left. If it's set to the right, the passenger stairs will not move, and loaders will, which is probably better.
Which is why, the current Live Update have all the supported planes that have a refuel point pre-configured by GSX, on the right side.
But of course, if you already customized it, your customizations will take the precedence so, either Reset the configuration (so it will revert to the one that comes with GSX, or invert the fuel position (make the X positive) in the GSX airplane editor.