2006 passat Help

[Jackie729]

Hello, I need some help I bought a 2006 Passat 2.0t with my boyfriend loaning me money along the way from rebuilding the front end to a tune ups and sway bars but now we have come to an impasse and we can't seem to fix it, any help would be greatly appreciated! SO what is going on is that my car hesitates or slips between gear changing(usually only 2nd into 3rd and 5th into 6th) with an automatic transmission the car runs great otherwise but then when driving anywhere from 15-30 minutes it shows a P in a circle with a line through it near the check engine light and then in the middle of the dash between the gauges on the led, it says Parking Brake Fault! Limp mode engages and I'm stuck in the gear that I'm in and I'm forced to continue driving that way or pulling over shutting off the engine and restarting it which fixes it. I live 45 minutes from work so it is basically not drivable on a daily basis, my mechanic is stumped and will not pass it for an inspection sticker so it's illegal until it's fixed anyways. I have pulled codes from a local AutoZone which were p0732 incorrect gear ratio and p0100 mass airflow which we think we fixed by replacing a hose . We also got a diagnostics test done and these were some of the faults found. (not sure if they are relevant)
ABS brakes - 00778 steering angle sensor, 01314 engine control module
CAN gateway- 00778 steering angle sensor
Immobilizer - 02829 enabling steering column lock from steering wheel electronics, 02827 Wake up request via esp
Parking Brake - 00532 Supply voltage b+, 00446 Function limitation due to under voltage. (we think we fixed with new battery)
Engine - 000768 random/multiple cylinder misfire 001287 idle control system rpm.
After we did the diagnostics we replaced the battery because the old one was the wrong one for the car and we also did plugs and coil pack to see if it would fix the misfires hoping that the misfires were the reason for limp mode but we were wrong. we think we fixed most of the problems but I'm still having these shifting problems and this "limp mode" problem, so again I would really appreciate any input/help. Thanks in advance!
Also I'm not 100% sure it is actually limp mode but when explaining it to my mechanic he thought that's what it most likely was it has full power just sticks in whatever gear the automatic transmission was in when the "parking brake fault!" showed up usually 2nd or 3rd gear I believe possibly only 2nd.
-Jackie