Been running since I was 12 and have done all distances up to marathon and can run a sub-90 min half. And still the first couple miles can suck. Accepting that and that it will get better will do a lot. On long runs where I warm up on the run, I ignore pace until well into mile 3. Legs are warming up and digestion is turning off —- it’s an uncomfortable experience. But it’s mostly psychological. You can run and run and run just below max heart rate* but you’ll be fighting yourself the entire time. Caffeine increases pain threshold so that can help too.

* should train using heart rate not pace since it accounts for humidity, elevation, and temperature and is what actually improves when training. For example, target running at 165-170bpm instead of 8min/mile because 8min is much easier in 50F than 80F with 90% humidity and your body may be doing the same amount of work at 9min on warm days that it does at 8min on cold days.