Mine is an early one of the new 4.20-inchers from last year.
There was an initial problem with the way Ruger was cutting the forcing cones, which caused leading in the cone & it built up severely.
Since corrected in production.

Mine has 880 rounds of mixed stuff through it without cleaning, after I had the cone re-cut locally. Couldn't do that with the first sample I had.
Very stiff DA pull as you've noticed, but I didn't buy it to be shooting DA and I won't bother to risk ignition reliability by fiddling with spring replacements.
Sometimes that works in the SP, sometimes it doesn't.

I'm quite happy with it & the sights are a great improvement over the older windage-only versions.
Denis