I might have a solution to your problem. I was actually having the same problem, but my frames did not drop as low as yours. Mine went from about 400+ to about 64, but anyway it has to do with sounds. They cause alot of lag when you are going in and out of the sound range. I would try getting rid of the sounds by deleting the files in your sounds folder, but remember to back up your .technicpack folder first. I hope this helps.
Regards,
rebelz0601