Having had a number of Makita reciprocating saws I can think of two problems that will cause the symptoms you describe.

1. A defective trigger switch.
Solution, change the switch.

2. Dirty on the armature.
Disassemble the motor and clean the contact surface where the bushes contact the armature. Begin by spraying the armature contact surfaces with "Contact cleaner" and if that doesn't clean it sufficiently you can rub the surfaces with an "Ink Eraser" to burnish the surface without causing excessive scratches or pits.

I have had problems with several of my Porter-Cable tools where the wire frays where it comes out of the tool. Part of the problem is that their cases require you to put a good bend in the wire to get it to fit in the case. I finally put insulated spade connectors on my router so that I could cut another foot off the cord and not have to worry about the wires on the motor side.

I've also had problems listed above and dust in the switch.