So you must pace yourself so close to what you can run.

As humans, we're designed to run about 20-22 miles and then you hit the wall. Taking walk breaks pushes that wall back so the marathon can be a pleasurable experience,

Again, it is not a good idea to lengthen stride, but use a lighter touch and quicker turnover. You can go faster that way. You might increase your forward lean slightly — that will increase your speed.

Going uphill, you do have to compensate by running slower. Rather than checking your watch (on a hill), go for the same perceived effort as you ran on the flats. I find the best way to do this is to monitor your breathing. If you are breathing more heavily going up the hill, shorten your stride.

Again, it is not a good idea to lengthen stride, but use a lighter touch and quicker turnover. You can go faster that way. You might increase your forward lean slightly — that will increase your speed.

If you run the same stride going up hill, you have to work harder. Studies have shown that as runners get faster, their stride length shortens. So quicker turnover is the key here. Paradoxically, a longer stride takes more energy, so you'll get into oxygen debt early.