Auto 4wd transfer case not getting into 4lo when hot

[Elherb]

I have a 99 tahoe with the auto 4wd. It will shift into 4lo fine when everything is cold and has been sitting, but after a long drive it won't engage. It tries, the motor attempts to shift, but it is unable to engage. I changed the fluid hoping that might help the issue, but it didn't. The fluid that came out was red. I replaced it with the correct blue auto trac 2 fluid. If I cannot resolve the issue then I would be going to swap the transfer case to a manual shift one. Any advice on resolving the issue with the current transfer case or advice on swapping to a manual floor shift model would be greatly appreciated. Thanks