We report on high-power operation of a widely tunable dual-wavelength Tm:fiber laser in the $2\mathrm{\mu m}$ spectral region using volume Bragg gratings and a simple resonator configuration for wavelength selection. The wavelength splitting range is continuously tunable from 1 to $50\mathrm{nm}$ ( $0.1–3.8\mathrm{THz}$ ), with $>115\mathrm{W}$ of diffraction-limited total output power for wavelength separations of $<40\mathrm{nm}$ . A maximum output power of $118\mathrm{W}$ was obtained for $279\mathrm{W}$ of launched pump power at $792\mathrm{nm}$ , corresponding to a slope efficiency with respect to launched pump power of 45%. The prospects for further improvement in performance are discussed.