Heater on 2013 r56 not blowing hot air

2013 CooperS, no problems to date. Suddenly noticed that I'm not getting
much heat--wondering if anyone has ideas, diagnostic/repair-wise. Here are
the details:

1) All of the following seems to apply whether or not I have temperature
control on or off.
2) The car takes an unusually long time to start blowing warm air (even then,
not hot like I’m used to with this car)
3) With temperature control on, it seems to act (mechanically) as normal:
when the engine first starts, with the thermostat set at , say, 74 degrees, the
fan stays on the lowest level—presumably to allow the engine to heat up. A
couple of minutes later, per usual, the fan speed increases—but it continues to
blow cool or, at best, lukewarm air.
4) A couple of minutes after getting up to highway speed, the air blown gets
warmer—though not up to usual hot level I’ve come to expect with the car.
5) Then, when I come off the highway and idle at a light, the air returns to
the cool/lukewarm state.

Any thoughts or suggestions are much welcomed! Thanks, Mike