finally, after a series of really bad (low) efficiency calcs around 50-60% i re-did somethings.
(might help some people out there in A.G land)
found out my thermometer was out by about 4C.
used a new bazooka screen (thanks to batz and his ideas)
despite stuffing up my sparge (went to fast) i've now managed to hit:
70% - according to Promash.
all i need to do now is correct my sparge (and remember the mash out) and i should be back on track to getting 75% +