At 4.5 to 5# the YS63 should jerk it back straight with any prop. Try the 13/6 and see how it compares to the 14/4. I agree with the others, either it is heavier than you think or you have an engine problem. It could be your engine is set a little lean and it shows up as lack of power while trying to pull vertical out of a hover.
If you are closer to 6# you are going to have the problem you discribe and the 63 won't be enough to handle it the way you would like.
The only time I've had problems as you discribe with my 5.5# pizazz is at our 1500ft field on a hot day. Pressure altitude of about 5000 to 6000ft.