whining in 1st during acceleration

2002 Express 2500, 5.7L, 4L80-E trans, 2WD. I have a problem with a whining/squealing sound only in 1st gear while accelerating. It doesn't happen in any other gear. What could it be?

First find out for sure where the noise is coming from.
Engine/transmission/rear end/drive line?

Is it doing it in manual low or just in low gear in drive?

It happens regardless of it being in "1", "D", or "3". I can't see the engine making a noise that suddenly disappears as soon as the trans goes into 2nd....same with the differential, axles, driveshaft, or any other part. Seem slike it HAS to be the trans.

Since it is most likely the trans why not just swap in a working one from a junker? Only other option is to do open up the trans.

It has been my experiance with junk from a junker you end up with junk from a junker.

It happens regardless of it being in "1", "D", or "3". I can't see the engine making a noise that suddenly disappears as soon as the trans goes into 2nd....same with the differential, axles, driveshaft, or any other part. Seem slike it HAS to be the trans.

If you have pinpointed it to being in the transmission.
Time for a rebuild or rebuilt transmission.

I would agree with you guys except for one thing. The trans shows no other symptoms of needing a rebuild. No slipping, no hard shifts, no clunking going in and out of gear, no overheating, no burnt smell from the fluid, nothing. The only thing it's doing out of the ordinary is the whining sound.

The first thing I would try is a fluid change. Not a flush. Just drop the pan and see what the condition is of the trans fluid. If it smells burnt (like burnt popcorn), then this can sometimes be evidence of damage. Also check for large pieces of metal on the trans pan magnet. Very small pieces are okay and even normal, but chunks of metal are a bad sign. If none of this is present, pop out the old filter, push the new one in and seal up your pan with the new gasket. Fill with fluid, start car, shift through all gears (P, N, D, 3, 2, 1, etc.) while keeping the vehicle in place, waiting a few seconds between each change. Drive vehicle, come back and repeat the shifting through process. After doing this, check trans fluid level and top off if needed. Keep in mind not having enough trans fluid can cause whining but having too much can also cause problems.

I would agree with you guys except for one thing. The trans shows no other symptoms of needing a rebuild. No slipping, no hard shifts, no clunking going in and out of gear, no overheating, no burnt smell from the fluid, nothing. The only thing it's doing out of the ordinary is the whining sound.

If fluid is good and filter is good and noise on low gear you have a internal problem.

The longer you let it go the more internal damage you will have.

How many mliles on transmission?
Has it ever been serviced?

126k on the van. I purchased it at 124k so I don't know anythign about the history. I'm gonna do a fluid/filter change tomorrow or saturday so I'll keep you guys posted. Thank you for your help.