So...I never thought I'd have to say this, but, the Springfield Line (New Haven - Springfield) has been a headache and then some for me lately. While some scenarios (mostly Career) run as intended, others (mostly Stanard) freeze after a few moves, or the locomotive glitches back and forth, popping in and out. I don't know what's causing it. I'm currently (as of writing) verifying the files. Maybe that's all I have to do.
Pick one of the locos on the VNHRR and do a Quick drive on any other route. If it works ok then do another Quick Drive with a DTG loco on the VNHRR. If the VHNRR locos are scripted then it might be the problem that others are having - see this thread https://forums.dovetailgames.com/threads/train-simulator-classic-launch-update.69927/#post-654923
Thanks. I never had this issue with the route before the Core Update. I'll try that. If it doesn't work, I'll switch to my other NA routes for the time being. Especially Marias Pass, since I've been on a BNSF kick as of late.