If you have your electrical problems resolved, drop the pan, pull the filter, inspect the pan for excessive metal, inspect the filter pad for metal, and check all the electrical connectors. You can change the PCS if you like, but the high line pressure may be a symptom rather than a cause. When the PCM detects a generic transmission slip problem (P1870) if will usually command full line pressure to compensate, and it sounds like your PSC is doing exactly what it is told.
It would also be a good time to install a drain plug in the trans pan so that future fluid changes are easier.cleaner. And there may be several future changes to clean out the trans and potentially restore operation.
Of course, if you find glitter when the pan is removed the game may be over already.