A conventional engine with a pulmore motor like the DT&I, needs more amperage than a can motor loco (not sure where the BK lies in that respect). And more amps require a larger gauge wire to pass amps to the motor.
The motor will run slow, and get hotter if denied amps needed. Voltage=rpm, amps=brute force, but there is some crossover too
18 gauge seems light to me. I'd start with beefing that to 16 or 14g and watch for an improvement. Running too large a wire MAY effect some command signal delivery But as is, this doesn't apply to you. Your LC is basically radio controlled with no commands on the track. So larger wire just means nice cool wire vs hot, more amps and less voltage drop per ft. (run the dti for a bit and see if the wires get quite warm/hot. If so; too small.
The DCS controls are not the issue and have no effect on conventional trains. Neither does LC control. The dcs might be limiting power (a meter the only way.... outside of a test light, it's dimness, and a guess.... but the command signals produced have 0 effect on old e-units and less than 0 on locos with switch only (no e unit)
It's either the locos have issue, or the track where it stops does, or the wire is too small for the draw.
A muti-meter is model RR tool #4 or #5
#1 being screwdrivers, #3 pliers. Tough call on nut drivers or a meter. Harbor Freight gives them away at times (coupons). You can even find super duper cheap analog meters at dollar stores that beat nothing.
If it is tube track, you might have a bad center rail isolator. These tend to only short as the loco passes over the track, causing te e-unit to cycle as the short eats all the power. It could be dirty or loose track pins as well. Tight? Or would the track fall apart if you lifted 2 pieces? Pressure at any connection greatly reduces the resistance there. They shouldn't be loose
