I was talking to Floyd Layton today and we were discussing how the Protroma seems to hunt.  We were talking about thrustlines, incidences, etc.  Floyd talked about some guys use a little bit of slop.  That reminded me of what I did for the Resolve, my previous electric profile.  So I did the same thing for the Protroma.

I used a Great Planes 4-40 ball link.  It is the same length as the Rocket City #87? links commonly used.  I then pushed out the ball using a pair of round nose pliers.  Then I screwed the ball link on the threaded end of the pushrod.
I cut a piece of 5/32 O.D. brass tubing to a length of 3/16.  The brass tubing od is smaller than the hole in the ball link.  This difference provides a small amount of slop.  Seeing the link is riding on a 5/32 diameter shaft, there is very little chance of wearing it out.  Here are 2 pictures that show the installation.  Very easy.

Did the play solve the hunting.  I know it works lots of times, but always felt like using play is just compensating for another problem.  Did you try motor downthrust?  Do you use stab incidence when building or not.   

Whoa
The idea of the positive incidence in the stab is to counter the prescession effects.  With a pusher prop the precession effects are reversed - and thus the incedence should be negative, not positive.

You might want to try a tractor porp on it just ot see if it has any effect on hunting.  If it does, then..... Retrim or rebuild might be in order.