the problem is the 3/8 has to leave that much stock or it will cut out places that you dont want it to. another words your endmill is too big for final rough pass.
use a smaller full rad endmil. as another step.
you have a finish rad. of .075 and alot of stock to hog out.
use your 3/8s for rgh then a 3/16 for a semi rough then finish with a 1/8, or you can just rough and finish with a 1/8, depends on how fast you run and how much stock you want to take off.