Also try Brewing Classic Styles by Jamil Zainesheff. It's loaded with simple recipes that will get you in the ballpark, and then you can tweak them to your liking. When you use someone else's recipe and you tweak it, it becomes your recipe.
That almost certainly explains the low attenuation, but not the ~30% mash efficiency. I didn't see anything about stirring - are you relying on the RIMS alone to mash in? What's the lautering setup? What was the pre-boil volume? It should have been edit: ~6 gal.