I was told to leave the truck in 2WD, but whenever I start it in the Morning?

Hello,

Auto 4WD operates in 2WD until rear wheel slippage is detected. So, you can leave it there.

My 2001 Suburban does the same thing, but I always put it into 2WD just because I don't want it engaging if I decide to floor it.

Auto 4WD uses a clutch pack in the transfer case. There is a speed sensor on the tail shaft of the transfer case that, when matched up with the front wheel speed sensors will be in 2WD. Once the rear wheels slip and the system detects the rear wheels moving faster than the front, it will engage a fork to put pressure on the clutch packs so the front wheel speed will match the rear wheel speed.

So, either one is fine, but I prefer 2WD myself.

Thank you,
Brendon