I was able to look at a Mike Wolf Big Boy and compare the centipede tender truck to the one on my DM&IR Yellowstone, which uses the exact same truck assembly. Both have the same wheel gauge (measured with calipers), with bushings to limit side to side movement on axles 1&5, with the middle three axles having no bushings, to allow them to shift as the truck goes around curves. The wheels on axles 1&5 on the Yellowstone tender have more side to side movement than the same axles on the Big Boy tender. Using a feeler gauge I could get a 2.5mm one between the wheel and bushing the Yellowstone tender, but barely got a 1mm gauge between the wheel and bushing on the Big Boy tender.
Here's the gap between the wheel and bushing on the DM&IR Yellowstone.
Here it is on the Mike Wolf Big Boy.
This could be causing the issue, especially if the 072 curves the Big Boy runs on aren't exactly perfect.