M104 loses power/ feels "stuck" after holding throttle

[isved]

Hello everyone,

I'm hoping to get some insight on a problem I am having in my m104(from '95 e320) swapped 190e.

The problem is as such:

The car drives fine. Shifts fine. BUT if I hold a gear (it's manual) and stay on the throttle (not necessarily full throttle) for longer than a few seconds, it hits a wall, and then seems like it's in limp mode. It still drives, but feels like something is "stuck" and is making it harder for it to drive. Literally feels like I'm towing something.
Note: I do not have a diagnostic module connected. I plan on getting one this weekend if someone says that it's directly related, but I am simply not sure.

Also, If I shut the car off and restart it (even if it's moving) it's right back to normal, until I choose to stay on the throttle to hold out a gear a bit longer than a few seconds. Maybe that will give the gurus some hints

Any insight is appreciated.
Thanks in advance.