Found a TSB for you Highbeam, it's number is 99-04-21-006
I typed it out just the way we get it from GM, hope this helps.
IMPROVED AUTOMATIC TRANSFER CASE FLUID
Models
99-00 Cadillac Escalde
98-00 Chevy and GMC K/T
99-00 chevy and GMC L van
99-00 Olds Bravada
Date 9/99
CONDITION
Effective with vehical production in late june 0f 99, all active transfer cases on the above listed vehicals have been filled with Autotrak II fluid, P/N 12378508(P/N 10953626 in Canada) .This fluid has a light blue color rather than the red color of the previous fluids and is the next generation Automatic Transfer Case Fluid. The fluid also cantains a better friction modifier.
On the models listed above, the active transfer cases should only be serviced usuing P/N 12378508 (P/N 10953626 in Canada) ,even if the original fluid was the red Autotrak II fluid. The previous fluid and new fluid can be mixed or topped off if necessary. The new Autotrak II fluid will be the only available fluid once the supply of the old red Autotrak II fluid is exhausted on units older than stated above.
The Owner's Manuals and some service information will specify the incorrect fluid due to printing the information prior to the fluid being introduced.