Dear customer Thank you very much for your clarification observing your query I do not know what procedure they did for the verification of the selenoids of the solenoids body and to the module of the gearbox, i mean the TCM (transmission control module), i observed that they have also replaced the wiring or loom that communicate the solenoid components with theTCM.
I recommend you to look for a second opinion do not stay only with the recommendation and the review made by the first technician, he hesitated to send you with an automotive electricity specialist, so I can question the revisions that he has made , because these revisions are ideal for a technician who has knowledge in automotive electricity, therefore I do not know the level of verification that he did, it is not because of doubting the capacity of the technician of your confidence, just that it is always good in these cases Find a second opinion when reviewing important components such as the selenoid body and the TCM.
On the other hand, if these components are in good condition it is necessary to monitor the oil pressure and oil temperature sensor of the transmission to verify that these are at optimum operating values. This is done by means of an automotive diagnostic equipment.
Also i noted that your transmission already has 70,000 miles means that it is already in time to carry out a replacement of transmission oil and filters so, I recommend that if you have not reviewed it, it is a good time to do so.
Dear customer If there is no problem with the viscosity of oil or with the filter clogged the problem that you are going to be presenting will be accentuated in the mechanized system of the transmission discs, to explain a bit how it works, your transmission is made up of certain discs and seals that are put to work in conjunction with the transmission oil pressure generator, when you have some kind of problem with some pressure drop or the wear of the seals and disks your gearbox or transmission gets into emergency mode and that is why you are always set into third gear, to solve these we have to carry a job to the transmission replacing all the discs and seals with a kit called the gearbox (transmission)master kit, this kit has all the components needed to do a deep work to the transmission if there is no type of internal blow or rip to the gearbox, we should do this type of work.
from my position it is complicated to to indicate with accuracy the problem in your transmission but I tried to give you an idea of how to proceed because you highlight me that you are stuck in your case. Any concern please let me know.
Have you understood me dear customer?