Do some brick sessions. I never felt the need to do swim-to-cycle sessions, but the cycle-to-run sessions really helped. I did Windsor Olympic this year. I did a sprint at Hever last year which is, by comparison, quite hilly.
I have a strong distance running record, I only really cycle about once a week in the season, I open water swim all year round.
Where I struggled was the last 5k of the run, surprisingly. Everything else was a breeze.
If you're going for as fast a time as possible, do more bike work as it's where you'll realise the most gains, and chuck in loads of hills. That'll help.
Does anyone have any exercises or strategies or advice on foot wear? I don't want it to get to the stage where I need an operation. I have stopped wearing my Nike Free's as I think they may have contributed to the problem. (I'm not slagging off Nike, they just don't suit me).