@Blake Morris no offense, but are you sure you didn't accidentally bend the side rods when installing the new tires? (This loco has long side rods that are all one piece, which dramatically limit how far the wheels and axles can slide laterally when rounding a curve.) Also, double-check the hex bolts that hold the rods to the wheels, and the orientation eccentric crank. If these are too tight OR too loose they could affect operation.
You might even take the shell off, place the loco on the track at the end of a tangent, and turn the flywheel by hand as the loco enters a curve to make sure nothing in the drive rods / valve gear is binding. Cruise control can camouflage a multitude of running problems!
I saw on your other thread, at least one other poster has experienced smooth operation on O36. Good luck!
