I had a local smith install a PRP "minor fitting" trigger on my XD-45. It dry fires OK, but at the
range, after a shot, the trigger doesn't consistently reset. After the shot, as I let off the trigger feeling for
the reset, my finger can come completely off the trigger w/o a reset, and I have to push it
forward. The reset is rather long  as well.

What are some likely causes that I can suggest when I take it back?

Start with the cheapest and easiest thing first.

First thing I would check is the trigger spring, take the slide off and manipulate the trigger. Does the trigger spring back when you let it go with authority?

Well...it comes back. I don't have another XD handy to compare it to.

They have a video on their site that goes step by step on the replacement process. Very easy to follow and do it yourself. I did and was very happy with the improvement. You can watch the video and compare your modification with it to trouble shoot your issue.