If I’m not on the gas hard my 7.3 powerstroke looses power from 40 mph to 50mph any ideas?

It has stage one injectors, k&n intake, 5in exhaust I put fuel cross over rail in it has the ya 6 position chip in set on 3. Tranny seems to shift fine if on it a little. I can hear the turbo up to the 40 mph then it comes back at the 55 mph. Turbo probably only has 20000 on it if that