Forget the trim in the circuit, unless you are doing lots of them. Trim neutral on the Base leg after your PUFA check. You will have a low power setting and won't notice till the go-around.
Correct, the Vref (Vth) is 76kts....that explains your floating as the Duchess has a well designed wing.
If you have lost rudder authority, as stated, you are in the flare too long and as you get close to Vso / Vs and (if you are holding off too much) you will find it hard to get her straight.
Secret is nail the speed on the approach 85kts; nice smooth level off over the threshold 76kts till 72ish; straighten with rudder while you can and cross control feeding in more aileron as you get slower (and hold it on).
Should be a greaser.
Don't forget if the xwc if too much, you can take a 5kt tailwind in the Duchess and indeed most twins.