Tenacity's preemergent effects are demonstrated when it is applied to bare soil, or areas of very thin turf, prior to seeding with turfgrass. If you have a reasonably thick stand of grass the Tenacity will not be able to work in this capacity.
Nimblewill (or Nimbleweed) is a warm season perennial. It is spread by stolons and seeds. Preventing existing nimblewill from seeding will reduce spread, and treating existing stands with Tenacity during the warmer months should remove this from your yard. Using a granular preemergent like Dimension or Barricade in the spring should prevent new nimblewill seeds from germinating.

has that mix ratio worked well for you in killing the nimbleweed ?

I thought it was 1 tsp per gallon ???

READ THE LABEL. The correct amount depends on what you are trying to do and what type of grass you are applying it to.