Agreed.I was not having any issues with GPS in the beginning. It was only after I tweaked build.prop that issues started to surfaced.
I think it does affect your phone if you keep restoring via TB. The best experience is always to do clean install, but most of us don't have that luxury, right?
What I will do is, wait for 9S (as 8S seems a bit buggy) and then do a full wipe and clean install...install nothing back from TB and see how the GPS is. So now just a matter of waiting for 9S which I assume should be out sometime near the end of the month or early January.