The issue sounds suspiciously like inadequate feeder and bus wires between the track and the power supply.
Way back when I was in college, the club layout had telephone wire (of all things !!) for the track wiring, no bus. Single or Double headed Mantua steam would stall on a grade with a heavy train, at full power (15V), drawing 1.5 amps; which indicated that the resistance in the wiring was the current limiter of the system.
Nfmisso, I as well think that is a factor. Now have 52 VA with a MRC 2600 and old Bues run much better but I know there are other factors that are coming to play.
First is the old Blues are running there stock Steel wheels, nickel ones should help a lot. Bus wires? Guessing they are the wires that go to the track. Some are only 26 gauge. Terminal strip for the feeders are not in the center of the board, some bus wires have a 15 to 20 foot run. Finaly what is propley hurting the most is the way the thottle is wired. Have the MRC 2600 sitting on the desk, then a wire to the celing then 3 foot and then down to the power strips that power the feeders. That is a 20 foot run and only 26 gauge.
I know better but never thought I would get this far into the hobby. Worst part is being a Audiophile, I know the power drop that small wires can cause. My stereo jumpers wires are gold plated pins and silver wires. Speakers wires are Monster Cable at 5 gauge. Yes, you can beat someone to death with them.
When I bulid the new bench, these short comings will be taken care of.
More power has helped, still need a lot of thottle, I am at 80% and running doulded headed SPD’s on the B line and a Super weight on the A line. Running a round 50 sMPH, crank it to 100% and they cook at around 85 sMPH.
Oh, the weighted SPD has power to the point it can spin the wheels, I did drop the train to 40 cars but doubled head they would pull 50 cars. At 50 the led engine was spinng the wheels. Why kill the old engine.
Cuda Ken