I just did my first axle fluid change at 16k miles. I noticed the oil draining out was quite foamy after a short warm up drive.
Is this usual? Didn't see much shinny stuff in the fluid, Filled back up with Valvoline Synpower 75w90. $7.99 per quart, Mopar was just over $20. It will be interesting to see how it comes out next time.
FWIW the oil in the front was not foamy at all. I am still confused about the switch to 75w140, I tow only occasionally and my trailer is relatively light for the truck (6500#).

 

Any idea what the level of it was prior to draining?

Niether of my diffs have ever been foamy, but the rear diff did have some sparklies in it at 18K miles.

 

Immediately after driving the fluid in the diff will be a little foamy, but will settle out in 15 to 30 min usually. If the foam is there more than an hour it is probably contaminated or broken down.

 

I don't think it's too much to worrie about. On my '04, I changed the diff fluids at 5K & the OEM fluid was a touch foamy. I think a little of that is expected. It get's frothed up pretty good. Considering your trailer weight and the amount of time you spend towing, I wouldn't worry about running 75w/90 at all, partcularly since you are using synthetic. It's tough stuff. One thing I would do is change the front to 75w/90 sythetic. The OEM goo up front is mineral (or dino) oil, I believe.

 

The diesel drive drain specialist at the dealer told me that frothing is from overfilling the axle.
I personally have no educated opinion on this.

Pete