Good that’s fixed, now while you’re waiting for that thermostat, check the TCM connector, is it tight? Any loose pins? Check to make sure the ground wire is connected and tight, you might have disturbed it while you where working on the temperature sensor harness.

https://www.obd-codes.com/u0101

 

It never occurred to list all current codes? Many are complimentary, and mean something when they happen together.

U0101 is another loose wire somewhere. You have to trace down which module on the CAN bus. One or more is not getting enough power or the bus is disconnected or the module is broken. In the case of a engine swap, my bet is the MAF didn't get plugged in. Usually your eyes can find the problem, if not here are a couple of links.