So a few weeks ago while driving my battery light and brake light came on. A few minutes later my van slowed to a crawl and could not start again. My battery and alternator were no longer working well enough, so I replaced them. Put my battery in backwards, blew the 80amp fuse behind passenger seat and the EFI fuse in fusebox. Switched those out. My radio died during this process... and still wont work...

Now I have a new alternator, new battery, new power steering pump, new transmission filter and fluid, and it starts up and idles great.
Unfortunately, I still have my battery light on, my brake light on, and it drives terribly. No power, goes into gear slowly and with a lot of hesitation, too crappy to drive out of the driveway.

I checked the codes, they read normal. I checked the alternator voltage, reads pretty normal (13.8 at the battery terminals at idle).
Any help would be hugely appreciated. Feels like a transmission problem but reads like an electrical problem.