Struggles to turn when in 4A

[postwick]

When I put the truck into 4A and drive slowly, it shakes/struggles when I try to turn, like is expected in 4H and 4L. I had the transmission rebuilt a year ago but I'm not sure if this is a transmission issue. Is there some sort of lockout for 4H/L that's incorrectly engaging when I'm in 4A, or not disengaging so 4A acts like 4H/L?

 

[twodollars]

Sounds like the t case is locked up. Have you ever changed the fluid in it? Might be worth a try. It should not engage unless the pcm detects slip and sends power to the front diff.

 

[postwick]

Sounds like the t case is locked up. Have you ever changed the fluid in it? Might be worth a try. It should not engage unless the pcm detects slip and sends power to the front diff.

I had the transmission rebuilt a year ago. Would that include the transfer case?

 

[bodabdan]

Not likely. It's a separate gearbox behind the transmission. Your front and rear driveshafts connect to it to send power to 2 or 4 wheels. It has its own fluid inside of it that should be checked and periodically replaced.
I'd like to think that whoever installed the transmission at least checked your t case fluid.