My 2001 4 runner has trouble shifting into overdrive from 50-62 MPH.

What is your question?

The car (175K miles on it)shifts smoothly through the first 3 gears, but when it reached 50-62 MPH, it "clunks" it's way into and out of OD until the car reaches ~62 MPH. Then it shifts into OD and works fine in high MPH. But if I decel back to the 50-62 MPH range and then accelarate again it goes through the same hesitancy. The mechanic replaced the torque converter, still happens. He tried injector fluid thinking it was a gas issue, still happens. Help please!