I have a 2015 Bounder 33C and the show is either cold or hot nothing in between. I ordered a replacement on the internet same quality. Who makes a quality mixing valve for RV's?
We also found that if you turn on just the hot water, let it get hot, then start adding cold until comfortable we didn't get the cold spurts if we turned it on and off ( we have that feature on our showerhead). Don't try to mix it to temperature like you do in a house. Try the above and see if it works.