We have Been working on this for a long time and are at whits end. Our tub does not drain or drains at a snails pace. Let me tell you what we have done maybe someone can think of something else.
We have replaced the tub and piping to the main. We have snaked the vents we have checked the pitch of the pipes and have checked the t where everything comes together. We have had the mains cleaned. We have used a ton of draino. Still nothing. Help!!!

What type of stopper does the tub have? Is there a drain cover with small round holes?

Remove the overflow plate, linkage, and bucket. Run water into the tub and see if that drains any faster.

It does have a cover with small holes and everything is new it's An American standard tub

No it does not

Did you do the test with the drain cover on or off?

You are "guessing". Why not call a professional who knows what he is doing? If what you have done has not cured it, then there is no way we can diagnose it without being there and doing our own testing.