misfire code P0305

I have a 1999 Tahoe (classic body style) whenever I tow my boat my SES light comes on and it will read this misfire code. (P0305) Does it mean that the misfire is on cylinder five? If that is the case which cylinder is number five. Any other info would be appreciated

Yes, Cyl 5 Drivers side of engine, 3rd plug back from front. 1357 on drivers side, 2468 on passenger side. Can also be an injector causing the problem.