1) I've run a LOT more this time around. In the past I've used an Olympic or a 70.3 a couple months prior as a warm up race. This year I used a marathon for which I basically trained by adding a lot of running miles to my spring. For reference I was running 35-40/wk in the spring, went down a bit after the marathon and have recently tried to get back up to that 30-49 range. My plan says I should be doing about that amount each week for the next three weeks. Also worth noting, the plan I'm doing this time around has somewhat significantly more miles in each discipline, though less intensity, than I've done in the past.
So in short, in case anyone cares: I'm currently supposed to be running 5 days per week (one of which is a short brick). I'm going to cut that back to three, cut the mileage from 35 to about 22 or so this week, and see how my body responds. I'll replace that run time with ride and swim time.
The first paragraph is good amplifying info. I think marathons take a hell of a lot out of our legs more than we realize. Odds are having done a marathon and with increased volume in the swim and bike, your aerobic fitness is going to be fine for your IM run. You're probably feeling the lingering fatigue of having done a marathon followed by intense IM training, in which case backing off the run is probably advisable. As long as you are able to continue strengthening your bike leg and come off as fresh as possible, I'd bet you won't see much fall off in your run in the race by backing off now.
As you know, a plan is just a plan.