Transmission Shudder 2007 PreRunner

My automatic tranny is shuddering while going between 4th and 5th gear.
If I manually go back to 4th it stops. The truck has 285K miles without ever changing the trasmission fluid. (I asked the dealer when I should check it back at 120K miles). They said "If it's not broke, dont fix it"
I have heard more than once that if the fluid is changed completely, I may end up walking.
Anyone experienced hits shudder? I cant imaging why new fluid would make a tranny quit working.

 

This isn't the first time I heard this from toyota dealers. many of them say it's a sealed transmission. Unless it leaks, then you have to change fluids. But i disagree. I say change it, and see ifthat helps with the shutter

 

It's only a $150.00 gamble. The dealer told me the tranny had to be at a certain temp to service it. Like within 10 deg F. Holy smoke batman. REALLY!!! From the looks of a pdf I got on the tranny, it looks like the fluid can only be sucked out. Ever had anyone tell you to only change part of the fluid? A mechanic told me that

 

Might find some info here http://www.tacomaworld.com/forum/te...hift-kit-shift-recalibration-kit-2nd-gen.html

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Good info you wrote there