  The Energetic Gamma-Ray Experiment Telescope (EGRET) experiment onboard the
Compton Gamma-Ray Observatory (CGRO) has provided the most precise measurements
of the gamma-ray sky to date. The EGRET measurements of the diffuse emission
across the sky show an excess above 1 GeV. This ``GeV excess'' has been a topic
of great debate and interest since its original discovery by Hunter et al. in
1997. We have modified the GLAST simulation and reconstruction software to
model the EGRET instrument. This detailed modeling has allowed us to explore
the parameters of the EGRET instrument, in both its beam-test configuration and
in-orbit on CGRO, in greater detail than has previously been published. We have
found that the GeV excess is significantly increased when previously
unaccounted for instrumental effects are considered. We will present a new
measurement of diffuse gamma-ray emission in the inner Galaxy.
