Given the weather you've experienced this past winter, I'd suggest that you not drill any weep holes in the thermostat. If you fill the system properly and use the two bleeders to purge air from the system there should be no problems with a standard thermostat. Weep holes will slow the warmup of the engine, even with electric fans, and may prevent reaching adequate temperature in colder weather.
The VSS or PCM could be an issue, but other things are required for the speedo to operate. The digital speedo module is powered by Fuse 15, so make sure that is intact. If the cruise operates and transmission shifts normally, the VSS is probably operating. The electrical connectors on the instrument cluster are also suspect.