This question is missing more information than it provides, so I am just
guessing at the requirements.  The question says nothing about the use of
the mixer, other than the viscosity.  So I have chosen a moderate level of
mixing intensity.  Under the circumstances, the fluid density is at least as
important as the viscosity.  The fact that the speed is specified may mean
that some of the equipment already exists, but impeller type and size is at
least as important as the speed.  Having made several suggestions, the
following is my recommendation.

The 3000 gal tank definitely needs baffles for that viscosity range.
Four wall baffles at 90 degrees about 10 inches wide would be expected.  I
suggest a four-blade, pitched-blade impeller, 40 inches in diameter with 8
inch wide blades.  The impeller will require about 2.25 hp, so although a 3
hp motor might be sufficient, I would recommend a 5 hp motor in case the
density or viscosity is actually higher than specified.