4.3L 4x4 - it shifts in and out of 4hi to 2hi and back fine when the truck is stationary, but on the fly it shifts into 4hi fine but when i press the button to go back into 2 wheel drive it takes between 30sec and 1min and then it knocks in quite loudly. i checked the vacuum pressure on the front diff actuator and that seems fine. it's not the actuator on the transfer case either. any ideas?

If you check your owners manual you'll see the same thing I saw shift on the fly should only be used going into 4 wheel you need to stop or even back up to go back to two wheel drive. I woodn't shift on the fly unless I have to as both ways the faster your going the harder it's on the parts. The loud noise is something hitting to gether that should be avoided. Going straight ahead at walking speed pust the button to shift to 2 wheel and then stop and slowly dack up to unload the gears and it'll shift easy and it'll last as long as it's going to.

Its the transfer case solenoid problem.But also get the TCCM checked.Transfer Case Control Module.The Transfer Case control module is the 'computer' located behind the passenger side kick panel. The Encoder Motor, sometimes referred to as the Transfer Case Shift Motor, is, as the second name implies, the motor that that shifts the transfer case gears. transmissions have shift solenoids/ a lock up solenoid(for the torque convertor) and epc (electronic pressure control)solenoid all these are for the trans itself not for the transfer case so if 4x4 is not working you have another problem.Transfer cases are located on the underside of the vehicle and are responsible for switching the vehicle from 4x4 to two-wheel drive. There is a switch located on the inside of this case that locks to cause all four wheels to turn or only two to turn. Also get the car scanned at diagnosis center to confirm the exact fault,there are many possibilities in this case,which can get faulty.Once the codes are retrieved the exact error part will be indicated,so you can go for right replacement. get car scanned at diagnosis center to get error codes, At diagnosis center you will receive the error code.As per the error code it will detect the exact faulty part in the car due to which the problem is occurring.For more help :--- at www.autozone.com its absolutely free to get car scanned.
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Hi! It can be a faulty transmission solenoid. You will need to have it replaced for it may reached it's break point sooner or later. Hope this helps and thank you for using FixYa!