mine don't overheat. i can idle all day.
u may have a worn impeller or a clog somewhere that idling doesn't push enough water thru the motor. get it check. a hot motor is a ticking time bomb just waiting to blow.
i haven't done it myslef but looking at diagrams n my lower unit itself(have a old spare one) the impeller is connected to the lower unit. drop that n it's right there to take off.
low water pick up is great bcuz u can raise the motor for optimum performance. but as will said, the down side is idling in shallow water n thru weeds the water intake will clog n the motor will overheat. lower water pick up is design for performance.