2001 Kia Sportage hard for car to go from 40mph to 60 mph

I checked engine performance - not sure of the root of the problem. When I am going uphill or especially trying to get on the highway, my car feels like it is pulling really hard to get from 40-60 mph. The dial thing will go up to over 4 where usually it doesn't go above 3. Once it gets over 50, the dial thing drops back down to 3 and the car runs smooth as glass.