One of the major causes of stuttering is insufficient VRAM. The 3070 should have 8GB which is sufficient in most cases. Although there are games that will push the limits on 8GB of VRAM and stuttering will appear. I have seen where individuals do not get the power connector pushed completely down and have a power issue, so you might want to check that. Also make sure you have the 6 or 8 pin CPU power plugged in as well.
If it ain't broke; don't fix it!