First of all: Nice Work.
I had a look on the google spreadsheet version.
I've noticed that you use "(430+SBV)*0.9" to calculate the raw damage of shield slam. (SBV= shield block value)
According to this sources (
wow-europe.com -> Shield Mastery talent explained and
worldofwarcraft.com -> Fortifications: post #7) shield mastery and 1h mastery both affect the damage of shield slam.
Perhaps you should include an option for shield mastery X/3, and edit the formula.
Imo "(430+SBV*1.X)*1.1*0.9" is correct. (with 1h mastery 5/5 of course)