The thermostat may well be bad, but have you looked around to make sure there's not a hot air register blowing onto it or a return air current that's artificially warming it above the cabin temperature? We had an issue like that with the mechanical thermostat in our Springdale. I changed the thermostat, it didn't help, then started looking and realized the floor vent was aimed directly at the thermostat. I turned the vent around and man was it much more comfortable
Maybe it's not your problem, but better to be sure than to spend money and find out you didn't need to.....
Good Luck,