Bought 2006 Sienna, 190+ thousand miles, but the trans is not shifting smoothly from 2-3.  Fluid had be drop/filled (not flushed) with correct fluid.  It has had a new radiator, and new battery.  It also has recently had 2 speed sensors changed which removed a CEL code (now no codes).  It has had a lot of other recent service, good tires (about a year), good brakes, plugs, and it runs well too.  It has about 196,000 + miles on it.  It is still drivable and runs good.  It still has been a reliable vehicle and has been driven several long trips over the last year, including being driven 1000 miles, and has been a Florida car so not rusty, but dash pad is cooked!  I have looked in to the problem.  Consensus online seems to be the U151E transmission (used on many Toyota models in the Mid to late 2000s) has issues it seems with this problem and the recommendation has been to drop the valve body and replace 4 of the solenoids relating to shifting (SL1, LS2, SL3, and SLT).  These won't test bad (via resistance) or throw a code.  It was recommended to use only new OEM solenoids but they are about $200 each.  I can get a whole solenoid kit (not Toyota branded, but made in US and may be rebadged OEMs, don't know) for about $450 that includes all 7 Solenoids.  The transmission specialist online recommended not to use a rebuilt valve body (which is about $300) because although the solenoids work, they will not likely function up to spec unless replaced.  Also was recommended to reset the shift learning for the transmission.  This requires a Toyota Techstream tool and to my knowledge other tools do not offer this feature.  Do you concur?  Or do you recommend another tool for a consumer like me?  Do you consider this beyond the scope of a non-pro mechanic?  Do you recommend selling it for whatever I can get out of it the way it is?  Do you ever replace on transmission solenoids yourself, or do you recommend a transmission shop?  I don't think it needs a complete transmission but I fear if I go to a transmission shop they will tell me it does (that is what they do).  I don't think I can justify putting a rebuilt transmission in it or could tackle a job like that myself.  I have successfully replaced a valve body fixing a shifting problem in a 2011 subaru.  I am nearby enough to you, I am in Evansville, IN (you are near Clarksville right? - so about 2 hours away (take I-69S to I-24 and east to Clarksville).