new thermostat question

I just replaced my thermostat in our 2008 Allegro bus. The only one I could find that works exactly like the original.  2 zones.  2 propane heaters. 2 roof heat pumps. After a couple hours use the front temp (zone 1) showed 75deg in the coach when it was about 40. Couple days later it now show 103deg. 103 is the max temp it will read. Thermostat is an RV Produucts or RV Comfort 20 model  8330* 331*.

My question: is the temp sensor bad or the thermostat bad?