Okay, I have done a lot of searching but only found one thread with this with this problem but had no resolution. So here we go.

Car: 1999 camry, U140E transmission

Symptoms: When shifting from 2nd to 3rd (4 speed) the tranny acts like it goes into neutral for about a second and a half. The engine revs about an additional 500 rpm then it goes into 3rd. It goes in firm, no slide, no slip. Its kinda like missing a shift with a manual trans and when it does go in it hooks up fast and firm like it should.

Background: This car was bought new by my aunt. Inherited by my sister then passed onto my daughter. This car has had an gentle life with regular maintenance and had a tranny flush and filter two years ago right before my daughter got the car.
The car has 144,000 miles and has not thrown a CEL and no codes. Spedo works fine.
I dropped the pan and everything is very clean with very little on the pan magnets and what was there was like what a fine dust would be. Filter was also very clean. The fluid looked good with no burnt smell, nice and red not brown at all.

My hunch is a slightly sticking solenoid or possible accumulator problem (worn or sticking).
Would just like some input before I drop the valve body for further inspection. I will post when the problem is resolved (I hate it when people don't post a follow up!)

 

From the sounds of things I think your hunch is right.
I wish I could give you some diagnostic advice but transmissions are one thing I don't regularly get into and I don't want to steer you wrong.

 

An accumulator could cause harsh shifting. The rev or flare could be caused by a clutch problem. There is not much you can do about the clutch.