I really don't want to jinx this but it looks like both issues are resolved...it genuinely feels like a different car. It starts differently, idles and revs differently, pulls differently throughout the rev band and even sound different, its not flat anymore. The power increase is immense I cannot begin to describe the difference between before and after. My old GTV 3.0 litre felt much faster than my GT before but now for the first time my GT feels like a proper Busso engine and a more powerful version of my GTV at that. However, I'm not counting my chickens until I've had it running like it is for a few days...
Just to recap there was a lack of power/flatness throughout the rev range and also a choking feeling under certain driving conditions (under load and part throttle) where it felt like it was about to release power but was being held back.
I've had lots of work done which hadn't resolved it, but the latest work, replacing the pre-cat lambdas has brought back all its horses in full glory and cleaning the throttle body seems to have sorted the 'choking' issue.
With regards to cleaning of the throttle body, I couldn't believe that such a simple fix could resolve an issue like mine, until I saw for myself the state of the throttle body, it was jet black all over, I had to use almost a full can of carb cleaner to clean it!
I'll pop an update in a few days, keep your fingers crossed for me, if this resolves it I have a few of you to thank for your advice and yet again it has to be said how much of a benefit this brilliant site is.