Electrical interior problems 02 envoy

I have an 02 envoy that is having various electrical problems. The temp gauge says -35 when its 70 degrees outside, the car does not always lock with the keyless remote, i suspect the odometer is also going bad due to a friend following me the other day and telling me that she was going 85 mph to catch up with me when my odometer said 70mph. HELP please.

Check for a loose ground wire or connection. You have several unrelated syetems going whacky. My first suggestion is to check for a loose ground with an ohm meter.