I'd echo the suggestion to check car weight. Harbor Freight sells a fantastic little electronic scale for ten bucks:
https://www.harborfreight.com/1000-gram-digital-scale-60332.html
I'm a car inspector at our club (which, unfortunately in this case, is HO), and we require all cars to be able to roll unassisted down a 2% grade. Common causes for high resistance are dirty wheels, worn or badly seated axles or truck frames, and wheels touching the carbody. I've had some luck swapping plastic for metal axles on some cars. We also reject cars that are more than 1/4 oz or so over- or under-weight.
HTH
Aaron
Overmod Just to clarify something: when you say you've been frustrated for 'a couple of days now' that your engines slip instead of pulling... does that mean this behavior just started a couple of days ago, or that you just started running N scale stuff on a new layout and observe it?
Just to clarify something: when you say you've been frustrated for 'a couple of days now' that your engines slip instead of pulling... does that mean this behavior just started a couple of days ago, or that you just started running N scale stuff on a new layout and observe it?