they stopped putting turbos in eclipses starting in 2000.
unfortunately, yes this is true. In 2000 they dropped the AWD and Turbo from the lineup. :(
how they get the extra 5 hp could be half a dozen different things
Its actually not from a half a dozen different things, just the compression ratio, and the intake manifold.
This difference is because the GTS's compression ration is 10:1 as opposed to i believe 9.5:1 in the GT. Also The GTS's intake plenum/manifold is shaped and designed differently, and it flows a bit better.