The inner loop has the same issues with these engines. I don't know if radius is an issue. Again, my MTH GEVO, which is just as long and has as many axles will run laps and pull 15-20 car trains around the oval with no problems at all.
Minimum radius for any of the GEVOs is 18 inches. Minimum radius after checking information on the trackplan is 19 1/2. 19 for sure at least. Found some tiny silver metal pieces on the track which I think is from underneath one of the IM GEVOs (I have them sitting on the foamboard on the layout) as I found some more pieces after moving them. It's kinda frustrating really, I don't spend a whole lot of time out there to begin with, yet everything seems to be falling apart. I might run trains around the oval for a few minutes at a time if I can and that's it.
The first thing I do with a new loco is clean wheels. You'd be surprised at the gunk you get off them. I use the 90% alcohol and paper towel method. It does wonders. Don't give up yet!
