I have a 2018 Peterbilt 367 tri- axle with an 18 speed with 32000 miles 510 horse. When I am in say 5th Direct and switch to over drive the engine does not come down any RPM it jumps into gear jumping the whole truck. Took it to Peterbilt they replaced the regulator and O-ring, If it was O-ring issue it would shift slow. This has been going on for the last 2 months. Only way to go into Over drive is push the clutch in then select.