I was really surprised at the quality of the GPM’s when I got them. They are definitely more robust than the stockers. Going from a 4mm to a 6mm shaft could certainly help with “bent shock shaft syndrome.” I’m running those crazy stiff Redondo Beach springs on them with 80k fluid and they’re holding up great. Of course my street bashers don’t get sent skyward, either.
Also, make sure that you haven’t eliminated chassis slap on landings. The guys that do this will never be able to keep shocks, shock standoffs, towers, etc. intact. A bit of chassis slap is a good thing, as it prevents all of that force from slamming the components upstream.