David Spirache

Hello everyone, before I start I just wanna say thanks in advance for any help.
I have a 2008 Audi A6 4.2 s-line

Let me start off by saying recently I have had a failed power steering pump, cracked radiator and multiple oil leaks that have been repaired. I started getting the PRNDS illuminated and disappearing about a month back, mechanic told me it was just a loose connection. Now recently the car will run fine for about 5min then the lights all get illuminated and I get misfires in cylinders 5-8. Injectors look good, coils are brand new. Every mechanic is currently stumped, it seems like my only option is swapping the motor or trashing it. I really don't wanna do either since I'm only a 20 year old college student and this car is practically the love of my life. Any help would really be appreciated. Thanks again!