Changed front diff but the whine is still present. I really need some help.
 

I just finished up changing my front diff because I had a nasty whine and grind when I let off the gas. Now the whine isn't as loud but it's still there. I drained out my old transfer case fluid as well while I was at, and replaced it with Valvoline 85/140 Durablend gear oil, and 85/90 in the front diff.

I've only had this truck about a month and I am unsure of it's service history, but judging by the cleanliness of the engine oil, lack of oil in the front diff I'd say it was severely neglected. I'm planning on changing the tranny fluid and filter tomorrow to see if that quiets it down, but I'm skeptical. What else could be causing the whine on deceleration? I did notice there is some play in the drive shafts between the front and rear, but I don't know what's normal and what's not. I really need some help on this one.

Rear diff oil also changed to the 85/140? U joints lubed?

As Savannah said, propshaft?

Some play in the shafts at the t-case is normal. Especially, once in the higher mileage club.

How many miles on the odometer?

Whining: Front Wheel bearings? T-Case? Tranny?

What color was the gear oil, were there any metal chunks on the drain plug.
As for the diff, better start looking for another one, used can be an inexpensive and good way to go. Might want to call Paul Grant, number below, he has a good selection to pick from.
As for your t/case, don't drain the oil till you find the fill plug, at the 11:00 area behind the brake drum and cable.

I got a great used diff from Paul Grant. I really had a hard time finding any wear on that sucker, and got it in without a hitch. I made sure to flush out the pumpkin to get all that gunk and metal out as well. The gear oil I drained from the T case was a very dark black color, and I replaced it with a little over 2qts of 85/140w Valvoline Durablend gear oil. There was some metal on the magnet of the T case, but not what I would call a large amount. I did see some flecks of goldish/copper color though, so that has me a bit worried. I'm gonna drain the rear differential today and replace the fluid with 85/90 durablend, as well as do a tranny fluid and filter change since as I said, I don't know the vehicles maintenance history, but I can tell you so far it hasn't been good.

I've heard that a dirty/clogged transmission fluid filter can cause a noticeable whine, so hopefully that quiets it down some. I have a bottle of Lucas Stop Slip to add to the fluid as well. I also inspected the wheel bearings and axle seals while I was changing the diff and all looked good to me, and the U joints looked in order and I re lubed them with some high temp bearing grease.

I just found out that when the wife took it to a local place that does oil changes, that they didn't check the transmission fluid while the vehicle was running so it could be low, even though the technician said it was fine. I guess he would say that since he didn't follow proper procedure in checking it. I've had this truck less than a month and all I've done is try to correct the neglect the previous owner subjected it to.

Also, how much of a whine is normal with these trucks? I've heard that a whine is normal, but does anyone have a video with a "normal whine"? I may be going crazy over nothing.

If they checked your ATF with the engine off, you can now be as much as 1.5 quarts low and take it back and have it filled while running.
You may find it wise to start doing your own services so they are done correctly, save a lot of money.
Have you had the front drive shaft rebuilt or replaced yet, do you know how to check it?

Mine only wines at over 15 in low range.

Mine whine is real dull. In drive, over 55 or so.