  We present broad-band (2 keV to 2 MeV) X-ray spectra of GRO J1655-40, a
luminous X-ray transient and occasional source of relativistic radio jets,
obtained with RXTE and OSSE. In one observation, the luminosity is found to be
18% of the Eddington limit, which is one of the highest luminosities ever
observed from GRO J1655-40. For this observation, we find that an adequate fit
is obtained when a broad iron line and a reflection component are added to a
model consisting of a power-law plus a soft excess component. The 95%
confidence lower limit on the rms line width is 0.86 keV. The power-law
component has a photon index of 2.72 and extends to at least 800 keV without a
cutoff. After this observation, a significant drop in the (5-12 keV)/(1.5-5
keV) hardness ratio occurred on a timescale less than 2 hours. From an RXTE
observation of GRO J1655-40 made after the hardness transition, we find that
the power-law index is harder (2.415 +/- 0.011), the flux of the power-law
component is lower, and the total luminosity is 10% of the Eddington limit. The
change in the power-law component is consistent with the correlation between
the spectral index and power-law flux previously reported for GRO J1655-40.
