If you want your first release U33c and/or first release SD70ACe engines to run better on layouts with less than perfect track work and/or cross-overs and certain switches here's what worked for me in both cases. Prior to these measures both types of engines had their sounds cut out or stall unpredictably on our club layout (used and abused Gilbert AF track, cross-overs, switches), but both ran without issue on my home layout (S-Trax). Both run fine now no matter where.
First release U33c - order two "without magnet" wheel sets 6408142051 at Lionel.com in their parts section. They cost $6.20 each. On the front truck remove the half wide pulmor band and replace it with the full-wide band from the opposite wheel. Remove the now bare (formerly full-width pulmor band clad) wheel by twisting it off the axle with your hand. Replace it with the solid steel counterpart from one of the replacement wheel sets. Repeat this for the rear truck. Reassemble and run to your hearts content no matter track conditions. You just vastly increased the engine's railhead contact and continuity.
First release 70ACe - do the same as above, but use the remaining steel wheels on the U33c wheel sets you already purchased. Those, however, you will need a gear/wheel puller to remove. Same too for the pulmor wheels on the SD that you are going to replace with the solid steel leftovers from above.
I did the above procedure to my SP U33c and my BNSF SD70ACe and both work interruption-free at home on my layout as before, but also now at shows on our club AF track based modular layout where previously I thought I'd never enjoy running them. I haven't noticed any difference in pulling power. In fact now, without parallel pulmors contending with each other, I'd say both engines run smoother at slow speeds through curves. You know, many Gilbert twin-motor PA's have diagonally opposite pulmors and they are often some of the smoothest running.
Those of you with latter release U33c's and SD70ACe's don't have any of this to worry about. Lionel refined both to run without interruption. In the case of the U33c the center wheels were flanged and in both cases I suspect Lionel added some capacitance to their circuitry to make them less sensitive to momentary current flow interruptions.
Have fun.
Run 'em if you got 'em.
They're trains, not trophies.