Might want to check the ECU for any stored trouble codes:
- http://www.4crawler.com/4x4/CheapTricks/index.shtml#TimingCheckConnector

High HC means the engine is running rich, check the O2 sensor, Air Flow meter and the ECU coolant temp sensor and also the thermostat. Could be the engine is running too cool. Also, what gears in the axles? With 31s, you should have 4.56 (manual) or 4.88 (automatic).