Gotta love GM "ingenuity" ...   
Check if the passenger-side operation is not affected.  A uniform problem usually points toward a weak battery in the fob.  If that's not the case, the contacts inside the pad are likely dirty.  That part is inexpensive and easy to R&R.  If you are handy, you can disassemble it and clean the contacts.  Watch out for the hatch button, it usually fails sooner due to turbulence of dust-moisture-yuckies.