Lionel 2021 Alco diesels

I have these engines and did not experience a problem.  Just FYI for you.

   I'd look to see if the coupler mounting portion of the truck needs tweaking. It really shouldn't rub the valance unless the track work is just plain awful. Neither should the turnouts make a difference on rubbing. 

  Since you run 0-27 you should keep in mind Lionel hasn't worried about that  diameter in quite some time. If it works on it your lucky. But binding side to side or couplers hitting steps is the usual issue. An unusual but possible issue would be rollers falling off the tighter diameter center rail (rollers, like a pilot, have an overhang too). Some O rollers can fall off 0-27 curves. I own two PW diesel switchers that do it. I limit the roller drop with a zip tie; this allows them to jump back on as two never seem to leave that rail at once.  I wonder if this is upsetting the Alcohol* trucks in a similar way too. They used to be very similar if I recall right. (Haven't actually owned an FA in many decades though, let alone one with  6-xxx prefix.)

  Despite rubber tires working well, I'm a magnetraction fan if for nothing else because it wont have a thrown tire to find and replace. I noticed that in the features listed itihas magnetraction. So I'd be reluctant to let it go unless there was exchange available. I'd look hard for the exact issue and address it myself if possible.

All misspelling and incorrect wording is courtesy of "smart composers" 

I sure wish hoop.la, Google or both would just give up on it. You can hardly read a page anymore without a computers stupidity making the human host seem clueless.

Mine has an issue entering the curve on my 072 switches. I have to run them straight through that location .