track power dip

The transformer is not the issue, it's the voltage drop through the track & joints.

I tend to agree, there is definitely resistance somewhere and track joints carrying power as the load gets heavier are going to expose it. In other words, a weak track joint and then many of them might be fine just running the loco, but when the sum of the load increases, then the resistance is exposed and the voltage drop is greater.

That said, I would do a check at the transformer first just to ensure there is not also a weak point in that ZW. Example, a known failure point is the common bus for the U terminals. They are just sort of riveted or staked posts through a strip of metal. With time, abuse, wiggling of the posts, they begin to pull through the strip and or just make poorer high resistance contacts. There is the internal breaker as well.

What I'm getting at is, take an 18V bulb and put it in parallel to your track feed right at the ZW output. Run the trains and observe the bulb brightness. If the train slows down the bulb is dim- the problem may be inside the ZW. If the bulb stays the same and the train slows down- put another bulb in right there at that spot in the track. Does it then go dim at the same point where the train is slowing to near a stop? How far is the nearest track feed from that spot in number of track joints?

Regardless of the amount of power that can be provided by a transformer, the laws of physics still apply. There is inherent resistance in track connections. Therefore, more jumpers are required. 

Let’s not forget the 1055 has neither Magnetraction nor traction tires. This loco is going to struggle to pull three of anything up this grade.

Steve

Steve makes a good point above about lack of traction on the 1055 - it is among the worst for traction that Lionel ever produced.

I can't tell from your description of the problem ("they can barely make it up the grade in either direction of the loop") if the motors are simply slowing down due to loss of power, or because the wheels are slipping? Can you please clarify?

George

Yeah, the 1055 was basically a gift horse, so I didn't peer so much into its mouth; we wanted a postwar diesel and this was the best we could do locally.  (This link basically says it all: https://www.tandem-associates....ins_1055_diesel.htm.)  But it does run reasonably well on a level surface. To clarify, the motors are definitely slowing down due to loss of power (or resistance to additional load/voltage consumption), not because of wheel slippage.  If I add more feeders/lock-ons, I'd be attaching them to elevated track on the trstle grade, since the others are placed at every six or seven track pieces on the layout.  Would that help at all?   Thanks for the input.

Before adding more feeders, I would invest in or borrow a decent digital volt meter (DVM) and test the voltage at several locations around the layout, both with no load and under load, and especially at the grade start and see what you get for readings. That should narrow the issue between power and connectivity/continuity or too steep a grade for that engine.   

@Richie C. posted:

...under load, and especially at the grade start and see what you get for readings...

Under load is the only meaningful measurement.