Slip out when in 2 wheel

If you are driving in 4 wheel drive on hard surface then you have drive line torque lock up as there is no centre diff to allow the front and rear wheels to equalise out the torque . 4 wheel drive is for use when on dirt / snow / ice where the differences between the front and back are allowed to slip the tyres . Jack up a rear wheel and allow the torque to dissipate by rotating a wheel . A point from all 4x4 manufacturers is that you NEVER drive in 4 wheel drive unless you are on dirt or ice/snow conditions. You have probably been getting away with it as any bump that lifts a wheel from the road surface will allow the wheel to slip. Even running the tyre on the white painted line on the road or any wet patch on the road will help ease the torque loading

check your oil level may be low.

your overdrive is slipping try a trans fix stop slip additive

It sounds like you are driving in 4wd drive on dry pavement. The front drive axles do not work like the rear differential. When you turn, the outside front wheel must travel farther than the inside wheel, therefore they are traveling through the turn at different speeds. If you are on dry pavement, this causes the gears to bind. You don't notice this on slick surfaces because the outside wheel will slip instead of bind up the gears. You should not use 4wd on dry pavement. That's the advantage of push button, or shift on the fly, 4wd. You can shift back to 2wd when you encounter dry pavement. All wheel drive vehicles don't have this problem because they have a limited slip front differential as opposed to a locking differential on 4wd. Hope I didn;t confuse you too much.

most likely the chain has streched and is slapping against the case and or jumping teeth on the gears either way it's not minor.

Normally while driving in overdrive (4th gear) you will feel it start slipping and finally slide into third gear. Then 3rd gear slips out into second, and you will never see 3rd or 4th gear again. I'm guessing this was the problem? If so its time for an overhaul

sound like shift motor is slipping trying to rotate sector shaft to go in gear.

Try reversing the car 2or3 times then go forward and try the box and see if it stays in then.
Let me know how you go Ron

Be sure that the truck is fully engaged in two wheel drive. It may have slipped out of gear on the transfer-case. Move the lever for 2 and 4 wheel drive back and forth a few times before shifting transmission.Good luck

What make, model, and year is your truck? Does it have AWD or just 4-wheel drive? What selector knob to you have for 4x4 (gear shifter or electrical switch?) Does your vehicle have limited slip or locking differentials? If you have an electrical selector with locking (limited slip) diffs and AWD, that is normal for it to automatically switch into 4x4 when you loose traction.