Glad the chuff switch worked out. I was having a hard time imagining it being much else.
Your other problem is a classic issue with some locomotives, it depends on the spacing of the rollers as a rule. I have several that do the same thing. For the steamers, I've added a pickup on the tender and connected it through the tether to the pickups in the locomotive. I also did that with an A-A pair. For diesels, one thing to try is to retrofit one of the dual roller pickups to at least one truck. You can also see if you can turn one pickup around to change the spacing, I was successful on a Williams locomotive doing that. You may have to scout around and find a different configuration pickup, I have one that I stuck one with a longer arm and it solved the problem. I did have to take a little metal off the truck to prevent it shorting to the roller, but the end result is it makes it over the switches fine.