That sounds great - in fact, I have managed to get my original circuit to work:

2 AA batteries ---> Step up to 5v to run RS232 level converter and LCD----> step down to 3v3 to run GPS and PIC

I had some problems, because the MAX233 ties its input lines to 5v. I externally tied them to a more helpful voltage, and now eveything works fine.

Out of interest, how can you up the voltage using PWM - did it use a voltage doubler capacitor circuit?

Cheers,

Ben