Check for DTC codes. If you get 81, 82 or 83 then check the power on the trans circuit, especially when powering up the truck. If it drops while the PCM is trying to test or actuate the solenoids in the trans the trans will default to 2nd gear (all solenoids off). The ignition switch is a common cause.
Also, if you notice issues with the tach or speedo, points to the same thing.
The Constitution needs to be re-read, not re-written!
If you can't handle Dr. Seuss, how will you handle real life?
Current oil burners: MB GLK250 BlueTEC, John Deere X758
New ride: MB GLS450 - most stately
Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6, '90 MB 350SDL, Kubota 7510