I can't say for sure without more info but I suspect
your [40psf] Live Load is too high.

I wasn't sure where the OP was located, so I erred on the side of heavier
snow loads. I've always used 30psf for live load calculations here in my
area. In any case, I calculated it with the 30 psf and still came up with
about the same size beam.

When we built our house, I asked the truss company to design for 50 psf
live loads, since we occasionally get heavy snow in the winter. Ironically,
the only change this required in the trusses was slightly larger metal
connecting plates. Kind of surprised me.

Anthony Watson
www.anthonywatson.us
www.mountain-software.com