Not an HVAC guy, but I have replaced several as well.
Is the fan kicking on and blowing cold air or not doing anything at all?
2 stage is just low heat and high heat (2nd stage). If low heat doesn't warm, 2nd stage kicks in.
2 stage should have 4 wires from furnace, power, fan, heat stage 1 (W1), heat stage 2 (W2). The Atwood diagram only has 3 for some reason. A 2 stage can run with a single W wire if W1 and W2 are jumpered at the control board (or thermostat if two wires come from furnace). Stage 1 kicks in and 2nd stage kicks in 10 min later if it hasn't turned off (warmed up enough). Looks like the thermostat is only 1 stage - only W1 - no W2.
I'd double check the wiring first no matter what it is doing. If the fan is blowing but no heat, I'd focus in on the W1/W2 wiring.
2018 Jayco Greyhawk 31FS