Auto Transmission ********"

The transmission has had no issues in the past, but did have the trans fluid changed around 2 years ago as regular maintenance. A few days ago it started slipping on the freeway, around 65-70mph. The engine would rev to about 3,000rpm very suddenly, then the trans would *****" back into gear very roughly and the rpm's would go back down to around 2500 or so. Even going at a steady 65, without braking or letting off on the gas, it would still randomly slip***** like this, maybe every couple minutes, give or take.

This does not seem to happen in the first 2 (maybe 3) gears. It seems to be mostly in 4th gear and the lowest mph that I have noticed it at is around 40mph.

Checked the fluid and the level is normal, color is deep redish-brown. Looks normal and no metallic specs can be seen.

I'm just wondering if anything could be causing this OTHER than the gears themselves. Perhaps electronic, or sensor related, etc.

One other thing that I noticed under the hood is that there is a vacuum hose that is coming out of the top of a case that appears to be attached to the side of the transmission. The tube is coming right out of the top of the case and goes over to the battery area, but just stops there, and it is not connected to anything (perhaps a breather?). It is very deteriorated and cracking, especially at the base where the hose clip attaches it to the case. Don't know if this is even critical, since the tube goes nowhere, but I thought I should mention it.

Anyway, I just want to make sure any reasonably simple options/possibilities are ruled out before I take it in.

Thanks so much for your advice!