So, it sounds like it's always at one end, and never at the other?
Try reversing the leads to the track. If the problem is a bad reverser, the problem will move to the other end of the reverse loop. If the problem stays at the same place on the track, then you have a problem with the gap.
It takes an iron man to play with a toy iron horse.
Put a loco in the middle of the loop. Leave it stopped, but with the lights on. Does the reverser work when nothing is crossing the gap, or is it always shorted?
Does the short happen at both ends of the loop, or only one?
Are you by any chance using a non-DCC loco for this test? DC locos do not work with auto-reversers.
Did you check the condition of the gaps? Anything conductive fall into them, or pinched there? Did you recheck your connections for security and cleanliness from input power to the track section controlled? Is there a reset feature...I have the unit, but don't recall if there is such a thing because mine has worked 100% since I installed it eight months ago and I haven't read the instructions.
Failing that, digitrax group on yahoo or call Digitrax tomorrow. Sorry I couldn't nail it for you.
http://dccspecialties.com/products/man_psxar.pdf
PSX-AR Manual
Page 7