I would consider replacing it......
Once drywall is left in a position, and is warped, the warping is
"memorized" into it.
Similar to bending sheetrock prior to installing on a rounded corner.
We wet it, and let it sag by placing it on a wall with a steep angle of
resting.
I was wondering if the rock was ran correctly, and like plywood, it has a
grain and a direction of run.
Also was ceiling board used?
Ceiling board is more rigid.
Also I consider a garage an un-climatized area and suspect to moisture....
Over the period of time, it may have taken on moisture and sagged.
Are the nails/screws holding it up well?
Usually a 2' on center ceiling is fine for sheetrock, if the rock is
properly fastened, ceiling board quality or 5/8",
and ran with the grain and or strength in mind.
john
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