C3MP69

A few days ago my 01 C3 which has the 4L60E left me on the side of the road. After driving for approx. 5 minutes I noticed after coming from a stop and going again it wouldn't shift out of 2nd into 3rd gear. So I tried to limp home because I was only 5 minutes away or so and then trying to go up a hill the truck acted like it was in neutral and just revved up. I parked it on flat ground, let it cool, checked the fluid. It was clean and fine I just did an entire fluid change for the driveline at 76K right now I have 87K.

The strange thing is after it cooled down I started it up and tried to see if it'd move and it did but wouldn't go above 2nd. This lasted for maybe 30 seconds and it started neutralling again. I did this all the way onto base because towing fees here are insane. Finally go to put it on a lift and everything underneath looks good, no leaks, no dents in the tranny or pan. Only thing I noticed with it running in park there is kind of a buzzing/rattling noise every 30 seconds or so it's not constint and because my exhaust is so loud I can not really pin point the noise.

No way in heck I can even afford to have someone pull the tranny and repair it. So i'm going to pull it myself and try to find some where here in Germany that will fix it and not cost me a crap ton. My question is if anyone knows what could be possible wrong and briefly what is all entaled in removing the transmission. Also since I'm pulling the transmission I'd like to throw in the Transgo HD-2 shift kit and a torque converter but not sure which stall to go with for my mods done to the motor. I can go pretty severe I don't tow and longest drives I do is maybe 2 and a half hours.

TIA!