jchaplain, I've read your post and I think you might need more down thrust.
If the plane climbs under power and dives on glide that usually means downthrust is needed.

You might also have an incidence problem.The plane shouldn't dive on its own.
If you don't have an incidence guage,let me know, I'm not to far from you,you can borrow mine.
I would like to know where you fly. I'd like to see it for myself.
PM me if you would like some help.
Paul