What is the specific issue with the lavender and tarragon? What do you do with them? And what goes wrong?

English lavender does well in zone 5 so long as it is in a sunny and well-drained location.

the issue is they die. I've tried different soils & amounts of water. full sun & partial shade. it doesn't matter.

Are you trying to grow them in containers? Both need full sun, lean soil and not too much water. Most plants are much easier in the ground than in containers unless they need some special soil unlike the native earth. eg Blueberries in and alkaline area.

Tarragon loves me, but I struggle with lavender. Tarragon needs a nurse plant to get established.

Place tarragon in part shade in front of a companion tree. The tree will keep the soil drier, and full of leaf mutch. A tree can also trick tarragon into being evergreen in Mediterranean climates.

If growing in a pot I add horseradish to get the same affect. Regularly add mulch.

Oh I just noted your zone, maybe full sun near tree roots would be good in your zone. But once tarragon is established it does well.

I 100% expected french tarragon to be an annual for me but I planted it very near my lavender (which is 5 years old) in a raised bed (designed for my herbs - mix of garden soil, potting soil, sand, and compost) which gets afternoon shade from a crepe myrtle. The tarragon has lived for years and years - slowly flopping over and trying to spread. I have a tendency to water "wrong" (lightly and frequently as opposed to deeply) but it seems to like it. I did add some Mexican Tarragon next to it this year and it promptly turned crispy and died. *shrug*