I'm not disagreeing with cleaning brush dust and lubing as this coincides with increased voltage needs (cars too, clean those wheels oil any that need it (wipe oil on rust, brush, oil, wipe, repeat until clean, wipe well with an absorbant cloth. A little oil "darkness" is protection)
Some locos I have won't wake up until they have warmed up. It's nothing new to me. Warm ups were rituals for Gramps. The loco would sit until smoke got cooking, then it would get a good two or three laps alone on an 18x30 at LEAST before it pulled a load.
I.e., yes I have to apply 100% of a 1033/15v 4a to wake up a few pre/postwar cast era locos. Some cannot pull a load until they warm up. They also get run at full throttle most of the time. (same trains on a kw fly around, pull 25+ cars (I only have so much room) and can jump rails)
However, some engines do need more voltage when they wear too. Look that the axles dont wobble fwd/back; shift away from the gears (needs bushings?) Also note how the gears ride on their shafts. Worn will tilt off plane once side thrusts start. Eventually bad bushings/gears can bind out of sequence/lock up, esp. 6 driver PW. (gearposts can usually live a longer life with prudent gear changes)