So I thought we had this licked when I had the thermostat changed....but...had the truck plugged in last night, (on a timer for 4 hours), started the truck up in the am and all seemed fine. Temp guage is slightly rising and then the dash guage shows no heat but I have lots of it coming out the vents. Stopped and restarted truck and dash temp guage working fine, have to go to the garage and get them to see what code came up as it through the check engine light this time, (had never done that before). This only happens after the block heater has been on for any length of time. Has anyone else had this issue or know what could be up? Thanks for taking the time to read this.