when reaching speeds over 50mph drive is sluggish and O/D light comes on? on 1997 Ford Ranger

auto trans, rear 2wd, 151k miles. OD light comes on as I approach speeds over 50mph. It feels as though the transmission is having difficulty shifting gears from 3rd to 4th? It has been suggested that my transmission need to be reconfigured. If possible, please provide me with an explaination as to what this means and possibly a price quote for service. Thanks.

Asked by for the 1997 Ford Ranger