The question is do any vendors restock on items after 3 days like fallout 3?

Yep, it's still every 3 days.

Sorry if it sounded like silly question just I looked it up and people are saying they don't but thanks for the answer.

Some of them don't seem to restock. I went to the bartender woman in goodsprings because I remember her giving me twice as much cash as most vendors, but she only had like 50 caps.

But others definitely do, like the Gunrunners, I go there as much as possibly to buy .45-70 Gov't hollow point, since I can't find that ammo anywhere else (either in standard or HP).

As long as some do I'm happy it like fallout 3 they did not all restock I just wanted to be sure