Someone suggested to use some kinda paste .. tooth paste???
Thermal transfer paste ( heatsink paste ). And a big heatsink.

And then what?
Go for a dedicated H Bridge using N and P channnel mosfets.
Using one PWM channel and some pulldown diodes ( from between the gates current limiting resustor and the gate, back to a PIC pin ), you can control where the PWM goes, hence dirn.
Andrew