[Driving piston will not return on Dewalt framing nailer]

I am borrowing it and hope to avoid having to pay service charges that are nearly the price of the gun itself. I would order new gaskets, but all of them in the trigger assembly and on the piston head seem fine.

[Driving piston will not return on Dewalt framing nailer]

Hey, I need to get my framing nailer working again asap. It is a Dewalt D51844. I am not entirely sure how the driving piston is supposed to return, however, it fires but wont return without being pushed back up. I've oiled the piston shaft and checked the o rings on the piston head and in the trigger assembly. Occasionally after firing it it will blow off air from the tip and slowly return back up with a comically long delay. The gun also started firing nails out uncontrollably upon connecting it to the compressor once and only once...

 

Any diagnosis or ideas? 

 

Running it at ~110psi with 22 degree plastic collated nails. 

 

This issue arose after driving at least 1000 nails without a problem.