Ok so today i went for a medium length run at a pretty easy and moderate pace. That being said i have recently been training by just feel alone seeing as im early in my training block for upcoming 70.3 in March. It felt very easy and could of maintained it for quite a period of time. It was my usual easy pace of 8:00 per mile. I got a new HR strap since my last one died and figured to use it today as well but when doing so my average for the run was 150 which is zone 4.0 for me and equated to 8:30 per mile pace. I just figured to run slower since was at a relatively high HR zone. Here is my question, should i slow down even more so i drop closer to zone 2 or just stick with my usual pacing and see the same times and my heart rate gradually get lower each run?

Here is a little background on myself:

I am a tennis professional and would say i have a relatively high level of fitness and maintain it throughout the year. Last year i was able to compete in two races an olympic and a 70.3 here are my results and splits:

Olympic: swim 26:54--1:47/100m
bike 1:07--21.67 mph avg
run 38:13--6:49 per mile avg
70.3: swim 31:00--1:36/100m
bike 2:31:06--22.3 mph avg
run 1:31:11--6:57 per mile avg

I now am transitioning into the tennis teaching avenue instead of traveling across the country and internationally for that matter playing. This will enable me to have a much more set schedule and more time available to train. I am trying to qualify first for ironman 70.3 championships and then step up to ironman full distance and then KQ. Any advise on what i said training wise based on feel/HR or anything else for that matter would be greatly appreciated thanks so much!!