Sorry you are going through this
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There are tons of shops and DIYers that are absolutely horrible!! Even these self proclaimed trans experts on YouTube do absolutely terrible work.
A very common problem with the 4R100 is the center support set up. One must take extreme care and follow specific steps in addressing the engineering flaws and reassembly steps. I authored a thread on cross channeling and posted it on this site. I also authored a thread on vacuum testing. You can’t just rebuild an old trans, not do vacuum testing on valving and expect hydraulic issues that probably caused the symptoms or damage that led to the rebuild in the first place OR have then rear their head down the road. You should read it. A step that is often gotten wrong is torquing the center support bolts as soon as the center support is installed. That should never happen like that. They should only be put in loosely until all components in the bore are installed and only then when the trans is then in the horizontal position. The valve body ledge above the center support must be then checked with a straight edge to check for case deflection. Failure to follow that procedure will result in the overdrive piston return spring preloading and the weight of the overdrive drum and coast clutch against the feed blots when the center support might not be exactly seated against its ledge seat in the case. This can result in case deflection and hydraulic cross channeling and or center support feed bolts loosening. You could just act like I did not educate you and ask them what torque do they normally set the feed bolts. Don’t act like you know anything just say, Some guys say there are different values or something like that. He will rattle off ten to twelve pounds. Then you ask, And of course you guys torque them as soon as the center support goes in? Don’t say a word. Let him answer.
Feel free to private message me. I can give you my contact info. I’m a diesel and hydraulic mechanic with 37 years experience. I am not soliciting you in any way.