sorry, but basically it sounds like the pan was the right speed and the boom up or down was too fast...and to make the boom "corrected" its gonna make more frames ( tween ) on the pan...which will make it look choppy...you know ? Its trying to make more frames in between ( tweening ) the pan, to accomodate slowing the boom...
sooo basically you have to live with it or eeek it slightly....like use "less" time duration to take the "curse" off the camera move, while not getting all the tweening where it looks choppy...
( your friendly neighborhood dolly grip )
Enable frame blending for the clip (right-click > Frame Blending).
If you don't get the results that you want with Premiere Pro, and you also have After Effects, you can use the more advanced frame blending options in After Effects. Basically, Premiere Pro has two settings (off and frame mix) and After Effects has three (off, frame mix, and pixel motion), where the third uses motion vectors to interpolate images between the original frames.
See "Frame blending".