Yes, you can shift between 2wd, 4 auto & 4 lock at pretty much any speed but I'd keep it below about 40 mph while shifting between them... it's easier on the transfer case and drive line... plus if you are going faster then that you shouldn't really need 4wd. To get into 4 lo you should be at a complete stop and have the transmission in neutral with your foot on the brake, switch the transfer case into neutral, then you can select 4 lo.I have 2wd, 4 auto, 4 lock and 4 lo. If I understand correctly you can shift between 2wd, 4 auto and 4 lock at any speed? The 4 lo you must be nearly stopped with the transmission in neutral? This is my first 4wd truck and I don't want to screw anything up.