I don't see sensors causing slippage problems. The TV cable adjustment might do it, the kick down cable also controls pump pressures.
Did you use the old torque converter or install the replacement tranny and converter?
Unless you emptied the fluid out of the converter, you may still have contaminated oil in the system. The converter holds around half of the total oil in the tranny, no way to empty it unless you remove it and dump it into a bucket or power flush the tranny.
I guess it si possible to have a stuck solenoid or one opening at the wrong time, never seen it, but heck anything is possible. Seems possible to have cross feed of actuating current between solenoids someplace in a connector, likely through moisture. Moisture in a connector may pass enough current, through the wrong path to cause issues.
Just a few guesses.
If the good one you swapped in was from a junkyard or unknown source, you may have swapped in a tranny with the same failure as the old one.
A shift cable adjustment may also be a possibility. Seems plausible if the shifter isn't hitting the detents and positioned half way between two gears, it may mess up the fluid flow. The master valve is positioned by the shifter, I really don't know what effect having the main valve in the wrong position might cause, it is unlikely to be good.