Nikon D700 Focus Issue

the Tamron lands that you have is a very sharp lens, and good value for the money. However I have that same lens and it will occasionally miss focus. I would not give you the advice to never buy third-party lenses, but rather if you do this is the type of problem you may run into.

If you are having this problem a lot you might send the lens back to Tamron. Also the advice of trying some Nikon glass to see if you get the same results is a good option.