Maintaining high rate rate during marathon

Heart rates vary a lot. Your numbers are naturally high compared to others, but that is not a problem unless you are/were ill with a viral infection, which obviously you weren't. You also did decent endurance training, which tends to lower the heart rate numbers from min to max, due to increased blood plasma.

You should not refer to heart rate during a marathon as a guide for any decision you make about pacing. The numbers do not correlate with training HRs at all.

Average heart rate during a (successful, evenly paced) marathon is a function of both economy and duration.

There are perfectly well-trained people who are either too old or lack the basic chassis to go under, say, 3:30:00 or 4:00:00, but they can't run marathons at as high a fraction of max HR as can a sub-three-hour type like you simply because the race is a much longer one for them.

If you do a lot of tempo runs or are naturally economical (shuffler type who doesn't waste a lot of energy bouncing or whatnot), you can run marathons pretty damned close to your threshold pace as long as you're fast enough. Frank Shorter is a good example of this.

I suspect that your max HR is a few ticks a minute higher than you think it is, but 88% of max is plausible for you.

i dropped off the pace at 16 because i felt like my heart rate was getting out of control. i always run my best when my heart rate doesn't get high (intuition). did you run with the 3 hour pacer? it seemed like they were going 3:30 - 3:15 for 6:45s.

yes, 179 is a/b 88% of 203 but that isn't an accurate measure. For example, if you are "training" at 10% of max, does that mean your heartrate will be 20 (10% of 203)? More accurately, you need to find the difference between your resting and max heartrate and go from there. If your resting is 50, you'll have a swing of 153 beats between resting and max. So running at 50% would be resting HR + (.50x153) or a/b 126bpm. You said you were at 179. If your resting is 50, then that would come out to (179-50)/(203-50) or 129/153 which is 84% of max.