Cummins Diesel Loss of Power

1998 Dodge 2500 4x4 Cummins Turbo Dsl 145k miles

Pulling a heavy trailer in heavy wind in 4th gear. About 2700 RPM at about 65 MPH with cruise on. Engine revs up a bit pulling a hill -touches 3000 rmp and suddenly drops to about 2200 rpm and 60 mph.

since then cannot rev past ~2500 or get ground speed over about 60 mph on the flat.

It feels like there is a wall at 2500 rpm. Feels like it does when fuel gels.

nothing "hanging loose" under hood.

truck runs great right to that spot. In lower gears can rev past 2500.

i blew something loose overloading I am sure - just cannot see what I blew loose.

Thanks in advance.