Using a 2026 locomotive that someone lent me to try to set things up for my grandchild.  If there are more than about 2 cars beyond the tender, there are places on the track where the loco wheels slip a lot.  In other words, wheels are powering forward at their normal speed but loco is barely moving forward.  I've tried cleaning both the track and engine wheels.  This loco, at least according to https://www.tandem-associates.com/lionel/lionel_trains_2026_loco.htm, does not have Magnetraction.  I've seen some references to traction tires but, despite having owned a Lionel as a kid, had never heard of those (mine may well have had Magnetraction).  I've seen discussions of putting weights inside the cab. And one discussion of whether the springs on the pickups are pushing the loco too high.  Any thoughts are welcome.  Thank you.