Close to the time to retire my 18 year old T100.
My 5 speed manual T100 had a vacuum actuated ADD. Would not disengage when cold. Some times it would not engage. It never worked properly until I removed it. Installed ASISN hubs from an old 4Runner, then removed the vacuum system and permanently shifted in the front differential with a mechanical modification. It's now a totally manual system and it works every time. I can also use low range in rear wheal drive only in tight spots like backing a boat down a long narrow ramp without it binding up. All I have to do is unlock the front hubs and then shift the transfer case.
No full size trucks available with a manual transmission. NONE! I am hoping for the 6 speed manual in the Tundra but it doesn't look good. All the big new automatic transmissions are too heavy, expensive and inefficient with all the locking and unlocking of the torque converters.
the Tacoma has the 6 speed manual with the ADD. Does any technical person know if free hubs can be put on the thing and the ADD disabled like I did with the T100. At least I and hubs so I can use 4WD low without the front differential locked to the wheels.
Manual is always better.