Changed the dashboard switch for 4wd. That didn't work. Still cannot get into 4wd.

Replace the shifter motor on the Tcase. Most common fail. Check the plug to it for corrosion.

The NVG 263 transfer case features a three button shift control switch located on the instrument panel. When the ignition is in the RUN position, the transfer case shift control module (TCCM) starts monitoring the transfer case shift control switch to determine if the driver desires a new mode/gear position. At a single press of the transfer case shift control switch, the lamp of the new desired position begins flashing to inform the driver that the TCCM has received the request for a new mode/gear position. The lamp continues to flash until all shifting criteria has been met and the new mode/gear position has been engaged. Once the new mode/gear position is fully active, the switch indicator for the new position remains ON constantly. In the event that the TCCM can not or will not complete the shift, the indicator returns to the previously selected position; this is a Transfer Case Shift Control Switch Indicator Flashes, then Returns to Previous Mode condition.
The New Venture Gear model NVG 246 RPO NP8 transfer case is a two speed automatic, active, transfer case. The NVG 246 EAU provides 5 modes, Auto 4WD, 4HI, 4LO, 2HI and Neutral. The Auto 4WD position allows the capability of an active transfer case, which provides the benefits of on-demand torque biasing wet clutch and easy vehicle tuning through software calibrations. The software calibrations allow more features such as flexible adapt ready position and clutch preload torque levels. The technology allows for vehicle speed dependent clutch torque levels to enhance the performance of the system. For example, the system is calibrated to provide 0-5 ft lb of clutch torque during low speed, low engine torque operation, and predetermined higher torque for 40 km/h (25 mph) and greater. This prevents crow-hop and binding at low speeds and provides higher torque biases at higher vehicle speeds, in order to enhance stability.