Hi GregK, what about if you use an Zener reversed bias on gate. Gate resistor about 200 ohms should work. As i can guess maybe PIC do not source enough current or voltage on Gate/source is below 2.5volt. It apear in some case that PIC are better to sink than source current. sp maybe buffer/driver might be insert before MOSFET gate.

Wich PIC do you use and on wich pin MOSFET are attach to.

24A load at 12V=288Watt. IRL2505 Pd=200w