After about 75,000 miles, I was about ready to EAT my second tranny. Had symptoms like it felt like it was slipping as it shifted between 2nd and 3rd gear, followed by a squeak/toot that resembled the sound of a squeaky shock absorber in an older car.
( Plus the down shifting is awkward and ocassionally when taking off from a dead stop it doesn't engage 1st gear too well ).

The first tranny was replaced under warranty at 35000 miles. It had exactly the same symptoms. But I waited until it died and I only had second gear before they did anything. The **NEW** tranny they put in lasted about 42,000 miles.

I had that one rebuilt last week... cost $2200 USD. It seems the Nissan dealer DID NOT change out the Torque Converter nor did they replace
the Solenoid Kit ( which affects the shifting )... just the tranny.

My newly reconditioned tranny feels like a totally different tranny now.
They replaced:

Overhaul Kit Friction
Solenoid Set
R/B Torque Converter
Direct Clutch Hub
Band
Filter
and they did a hot oil cooler back flush
and added some Lube Gard condtioner to the new ATF

Unbelievable... This is now the 3rd tranny in this car. And it
hasn't been abused. It's been maintained.
go to http://www.b15sentra.net/forums/
and search for Automantic Transmission if you want more details.
I'd be happy to respond to emails.

sorry to hear about ur troubles... next time, go with standard my friend.