Up and running again after a night's sleep and reprogramming the chip again. For whatever reason, which I cant work out, it works again. Probably some setting somewhere I got wrong.
I had made the if - opfreq change also , just forgot about it.
I did make a couple of other hardware mods in the end. 2m instead of 1meg in the sidetone line to try to knock the volume back a little. Im sure there are better ways to do this. and I parallelled an extra resistor on the mic bias resistor as I only had 0.8v going into the electret which I thought might be a bit low. I have 2v now.
Wouldnt mind knocking the side tone down a little for headphones but its a good vol for a small external powered speaker.