IIRC, proportioning valves are only for front-rear brake proportioning, not side-to-side (and are, strictly speaking "hydraulic" parts, not "mechanical"). In general, all braking systems are designed so that each side of an axle gets the same braking force; front-to-rear braking depends on other factors. I doubt the proportioning valve would cause this symptom.
Obvious things: Bleed it again (thought it sounds like you've covered this). Make sure all slide pin surfaces have the correct high-temp grease (and NO grease is anywhere near a pad surface). Make sure the pads are able to move smoothly where they're supposed to within the caliper.
Hmmm - It pulls to the right when *not* braking, or *only* when braking?
If only while braking,your new caliper is working really well - and the other one might not be. Take a closer look; it might need replacement as well.
If only while *not* braking, something is dragging or something changed (that shouldn't have) during the installation.
Also, in general, always replace brake pads on an entire axle, not just one side (original post only mentioned changing passenger side pads).
