Thanks everyone for your suggestions. I went with the 300s based off of spine charts and the Spine Calculator, taking into consideration that I am shooting 300 grains up front. However, the false read of a stiff spine bouncing off the rest sounds very plausible.
The problem is, I started with a full length shaft and cut away a fair amount of the nock left which, to me, means that it started weak and I stiffened the spine by shortening the arrow. Tonight I am going to shoot a full length shaft again and confirm that it is, in fact, worse than the arrow I am working with now. If it all looks the same then you guys are probably right and it is too stiff to start with.