My first question concerns the frame area at the cylinder stop. That dishing is something that would be quite easy to overlook when looking over a new or potential purchase. Are you 100% certain that was NOT there when you shipped the revolver back to S&W? I ask only because I don't see any need for a technician to be doing anything in this area and suspect this may have been present when you purchased the revolver. Not that it matters, IMO that defect is unacceptable.

That dent on the frame window under the barrel is also unacceptable and noticeable. Unfortunately that is not a defect that can be repaired easily because the only means of "repair" is to remove material with a file, probably by hand. The end result of this "repair" will be a frame window about 1/32 inch wider and I doubt that S&W still has gunsmiths who have been trained and fully qualified on Flat Filing properly. Yeah, Flat Filing is a Skill and something that takes a lot of practice and "coaching" to do properly. Most people who attempt to Flat File a chunk of steel end up with a domed piece of steel. What I am telling you here is that if S&W repairs this defect DO NOT lay a straight edge on that surface when you get it back. A little bit of doming won't have any effect on function and if it looks fine it is functionally fine.

As for your revolver shooting high with 255 grain bullets, that is simple the result of Physics and the only solution for that is adjusting the rear sight lower or installing a taller front sight. What is happening is that a heavier bullet moves SLOWER than a lighter bullet when operating at the SAAMI specified pressure. That slower bullet takes LONGER to transit the barrel and that results in an extended recoil impulse with the barrel pointed higher when the bullet exits the barrel. So, you have two options to correct for this. One is to change your sights, the other is to change your Sight Picture.

I will also note that changing how you control recoil can also effect the relationship between the sights and the point of impact. I once did an experiment with my 6 1/2 inch model 610 to see how much effect recoil management has on the POI and it's a lot, actually more that one would expect. Note, I keep a J Point reflex sight on the 610 so it's an excellent long range revolver. Firing off a sandbag rest at 25 yards I shot one group at the bottom of the target while controlling the recoil. Then I shot another group while allowing the muzzle to rise freely. That resulting group was 12 inches higher. As a result I can now say with absolute certainty that how you manage the Recoil of a handgun WILL effect where that handgun hits. So, if you shoot enough rounds downrange to start to fatigue your wrists and hands your accuracy will degrade and it's not due to "fouling" it is due to your just getting tired.