2006 Ford Ranger 4x4 FX4 with automatic transmission.
Engaging 4x4 is not a problem but will disengage while in use. Let off the throttle, Stop the truck and 4x4 re-engages.

If anyone has any suggestions what to look at it would much be appreciated
thank you

 

Welcome to the forum

Assuming electric shift transfer case?

Have you tried 4low to see if it also slips out of 4WD?
Have you changed the shift motor recently?

In the shift motor housing are 4 contacts that tell the 4x4CM(control module) when transfer case is in correct position, 2H, 4H or 4L

Looks like this on transfer case shift rod: https://www.therangerstation.com/tec...ft_motor-2.JPG
In picture transfer case is in 2WD(2H), shift rod triangle pointed at 2H

So when you select 4high, as an example, the 4x4CM powers the shift motor until the contacts show 4H position has been reached
But maybe the contacts are off a bit, so transfer case is not "all the way" in 4H
You can select 4high on the dash, turn off key
Then pull off the shift motor and have a look where the shift rod is pointed, directly at 4H or a little off to either side
If its pointed directly at 4H then your problem will be inside the transfer case, worn shift fork or ???

 

Truck does the same in 4 low. But you have given me a place to start.
thank you sir