  We present three-dimensional kinematics of Sagittarius (Sgr) trailing tidal
debris in six fields located 70-130 degrees along the stream from the Sgr dwarf
galaxy core. The data are from our proper-motion (PM) survey of Kapteyn's
Selected Areas, in which we have measured accurate PMs to faint magnitudes in
40x40 arcmin fields evenly spaced across the sky. The radial velocity (RV)
signature of Sgr has been identified among our follow-up spectroscopic data in
four of the six fields and combined with mean PMs of
spectroscopically-confirmed members to derive space motions of Sgr debris based
on 15-64 confirmed stream members per field. These kinematics are compared to
predictions of the Law & Majewski (2010) model of Sgr disruption; we find
reasonable agreement with model predictions in RVs and PMs along Galactic
latitude. However, an upward adjustment of the Local Standard of Rest velocity
Theta_LSR from its standard 220 km/s to at least $232\pm14$ km/s (and possibly
as high as $264\pm23$ km/s) is necessary to bring 3-D model debris kinematics
and our measurements into agreement. Satisfactory model fits that
simultaneously reproduce known position, distance, and radial velocity trends
of the Sgr tidal streams, while significantly increasing Theta_LSR}, could only
be achieved by increasing the Galactic bulge and disk mass while leaving the
dark matter halo fixed to the best-fit values from Law & Majewski (2010). We
derive low-resolution spectroscopic abundances along this stretch of the Sgr
stream and find a constant [Fe/H] = -1.15 (with ~0.5 dex scatter in each field
-- typical for dwarf galaxy populations) among the four fields with reliable
measurements. A constant metallicity suggests that debris along the ~60-degree
span of this study was all stripped from Sgr on the same orbital passage.
