NP 208 Woes

[72k20Farmtruck]

Hi all, i have an 82 k20 with an NP 208, and I just drove from spokane to portland with it. Driving off the freeway (hard braking) it felt like the tcase was popping out of 2hi. I plan on driving back to spokane on sunday, Is there anything I can do to mitigate this? To give some background, the truck is an old 6.2 diesel that has been swapped to a vortec 454 and 4l80e with original tcase (~250k miles). I have taken the truck on many very long trips (2,000 mile and 5,000 miles etc) with no issues. Drive it ~350 miles and it decides to act up now? Any input is much appreciated. Thank you.