"Adjusting the lift control knob on my 2305 changes the down speed but not the up speed."
Good point...
Briwhit, unless you think the tiller will bounce more than 1.5", it should be okay. How is the shaft length when it's on the ground? If you run through a rut (tractor rear goes high while tiller stays low), is there enough play to keep the shaft together?
Edit: That little issue can be remedied by putting the 3ph lever in the 'neutral' position.