Hi, @
Honcho.
In order to keep your thread clean, thought about sending this through PM but as others experienced similar issue, please allow me posting here.
First of all, have never installed the caliper service kit especially the dust boot from Centric and I don't even know whether it has the same design as the OEM one or not.
Only used the OEM one in my life (but done 100s of them) so could be completely wrong but from your photo, it looked as if the dust boot is not seated properly inside the caliper bore.
Please allow me using and editing your original photo.
Yours is on the left side.
The largest diameter section of the dust boot (marked yellow) should sit within the bore opening, like on the right side.
With the similar piston position, you have fair amount of gap (marked red).
You may want popping out at least one of the piston to double check the boot seating.
The base lip should be inserted and sit inside the narrow recess of the bore (marked green).
Hope I'm wrong.
Kaz