  We present a five level atomic system in which the index of refraction of a
probe laser can be enhanced or reduced below unity with vanishing absorption in
the region between pairs of absorption and gain lines formed by dressing of the
atoms with a control laser and RF/microwave fields. By weak incoherent pumping
of population into a single metastable state, one can create several narrow
amplifying resonances. At frequencies between these gain lines and additional
absorption lines, there exist regions of vanishing absorption but resonantly
enhanced index of refraction. In $Rb$ vapors with density $N$ in units of
$cm^{-3}$, we predict an index of refraction up to $n \approx
\sqrt{1+1.2\times10^{-14}N}$ for the D1 line, which is more than an order of
magnitude larger than other proposals for index of refraction enhancement.
Furthermore, the index can be readily reduced below 1 by simply changing the
sign of the probe or RF field detunings. This enhancement is robust with
respect to homogeneous and inhomogeneous broadening.
