I guess I'm at a loss here. You say everything is up to spec as far as the pressure goes. No loss of fluid, you are fully charged up. You measured temps in the mid 50's. Ok...what temp do you think is correct? What was the ambient temp inside the cabin and outside? Is the blower not blowing strong enough?

If you're getting good pressures, and no leakage, then your compressor isnt going bad. R134 isnt known to be as cold as the old R12. I dont know about you, but I dont like to drive around with my interior in the mid 50's, that's pretty cold.