Redfaction

hello, so i have a Audi A6 C5 2001, and i started having this problem after shifting out the straight pipe with a catalyctic converter, the car got alot power back, but after passing 3,5k rpm in first gear the car just died completely. and by this i mean everything died,. no light, no ignition, no dashbord light, nothing at all. it's just like the battery was pulled out. after 3-5 mins the car got it's electricity back, and started right up, i drove it nicely for 5 mins no problem. not exciding 3k rpm, after 5 mins i shifted into second gear gave it all i had, and just around 4,5k rpm it died again, no warning, the car pulled hard as it should, and died. no warning at all!

after wating 2-3 mins it came back, no dash lights (engine light / Abs ) no problem. i took a cheap OBD2 scanner and it only came up with one code, P1602, but i'm very confident this is because i took of the bettery terminals, and put them back on. so if i drive under 3k rpm it's all good, no hessitation no problem what so ever. i have no idea what to do.

i took a multimeter on the battery 12,68V after 12hours while it's in the car connected, and 14,2v while idling.. i wonder what can cause this, if i drive on a bumpy road, like a horrible gravel road, the car jumps and shakes a little but, but as soon as i slam the gas pedal to the metal, it just dies. no shaking, no nothing. and the whole car is completely dead, even the emergency light switch dosen't work. if i switch the lights to park, no nothing. no power at all...

im sorry if this got a little messy, my English is not the best, but i hope some of you know the solution to this problem i'm having!