It sounds "normal" to me.
The Boss 6.2 engine in my 6 spd F-350 shifts to direct (4th) when it needs to pull.
It runs at 3500 or less rpm 95% of the time in rolling land carrying a 3200lbs full height truck camper while towing a 4500lbs enclosed barn trailer. I usually lock out 6th - tow speed of 60 - 65mph is easy to maintain in 5th and 4th without the constant shifting in and out of 6th.
It is happier on 91 gas vs 87 when towing.
If it wants to downshift to frantic mode I select manual mode and hold gears without running the engine to the red line.
Manual mode is available with cruise control on - it's a nice feature.
