Originally Posted by BritM5
Lately, its been refusing to engage in D or R, after being stopped at a light for example. I've also noticed that at times the engine runs at inexplicably high RPM (sport mode) when stopped at a light also, for example.
The problem mentioned by @PowerSource
typically manifests when you first start up the car. The usual symptom is that the "Start" light flashes instead of staying on and the car does not respond to pressing "D" or "R".
From your description, it sounds like the problem is manifesting while you are driving the car, not when you first start it up. If that is the case, the problem may be a weak or unbalanced cell in the main battery. Obviously, it is impossible to rule anything in or out based on this description and whoever looks at the car should consider all possibilities before making a diagnosis.
Can you clarify a bit further? In particular, are you switching out of "D" while waiting at a stop light and can't get back to "D" again? Or are you having problems while you are driving around?
If the car is located in Miami, and can still be driven, you should consider taking it to @Harleyguy
while it is still moving under its own power.