I did try going up a size teat last week and it made no difference - the strange thing is she only gets really fussy like this sometimes, not all the time. In fact just her last feed I struggled to get 70mls into her - less than half her quota. She weighs 5.5kg. She NEVER drinks her quota, so when it is such a small feed, I really start to worry.
There are definitely no lumps in the teat and I always check the flow and the temp...