Should Mechanic have found that the TCM needed replacing B4 Trans Rebuild?

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My Mechanic told me I needed a rebuilt transmission. Long story short. 7 weeks after taking the truck to him and 2 rebuilds in which he rebuilt it twice, he now tells me the TCM is bad and wants another 1500.He is claming that the faulty TCM didnt show up when the codes were ran.They are holding my car for ransom. I called 2 nissan mechanics and the BAR in Culver city. They all agree he should have found the problem with the TCM first. But he wont budge. (FYI) 7 momths ago the same mechanic replaced the Valve body. That lasted about a week b4, he claims, pieces of metal from the bad tranny caused the newly installed valve Body to malfunction. Its a nightmare