Dave,
I think it would be great if you can stay with the R134a.... Comfortably.....

Of the things you have changed out....the P condensor may have only offset the reduced efficiency of the R134a...

So, since we know that ' airflow across the condensor' is the primary limiting factor in ANY AC system....

Why don't you put one of the high performance Aux fans on your system before you make the decision on switching back to R12 ?
See if that makes the difference on keeping you cool with the R135a ?