the aoa is rising which causes drag to skyrocket.
unload the stick at low speed, when practising stick it in a flat turn and check the aoa gauge. 15 units at 330 knots is the sweetspot, then pull harder which will drop the speed, watch what happens to the aoa when you get below 300 knots, youl see it climb which will cause more speed loss and so on.
it really does just come down to practise