tach = ignition coil
not always only on the V6 because on that model the tach is feed by the coil on others it's feed by the ignitor in the dizzy.

speedometer/odometer= speed sensor not always the case if one or the other is working it's most likely the speedo ,the 5th gen speedsensor is pretty trouble free I still haven't replaced one yet...but on the 4th gen 99.9% it's the speedsensor as the CEL and flashing D4 or S light is a giveaway.