Not enough power.
Your choices are:
1) replace the old 6 car with the new one. It has WAY better power.
2) Upgrade, or have upgraded, the old 6 car with the Simple-H power output hardware
3) perform a Master/Slave mod to add the power of another base into the power controlled by the main one.
Of all those, I would recommend getting the new 6 car base, the "APB" as it is known. C7042. It's not the cheapest, but it is the easiest, and gets you quickly up to date with the latest and greatest hardware.
The second, you have a choice between paying almost as much as the new PB, or doing it yourself. If you're handy with surface mount components and a soldering iron, you can save some money by DIY, but the Simple-H hardware isn't cheap to begin with.
The final option is the cheapest, but by no means the easiest. You'll need to be handy with the iron again, and it's a risky project if you do it wrong.
What I don't know is why it seems that the power has gotten worse over time. I can only guess that the mosfets are degrading somehow for some reason. RichG, RikoRocket, or others may have a more educated and experienced answer, though.

Your choices are:
1) replace the old 6 car with the new one. It has WAY better power.
2) Upgrade, or have upgraded, the old 6 car with the Simple-H power output hardware
3) perform a Master/Slave mod to add the power of another base into the power controlled by the main one.
Of all those, I would recommend getting the new 6 car base, the "APB" as it is known. C7042. It's not the cheapest, but it is the easiest, and gets you quickly up to date with the latest and greatest hardware.
The second, you have a choice between paying almost as much as the new PB, or doing it yourself. If you're handy with surface mount components and a soldering iron, you can save some money by DIY, but the Simple-H hardware isn't cheap to begin with.
The final option is the cheapest, but by no means the easiest. You'll need to be handy with the iron again, and it's a risky project if you do it wrong.
What I don't know is why it seems that the power has gotten worse over time. I can only guess that the mosfets are degrading somehow for some reason. RichG, RikoRocket, or others may have a more educated and experienced answer, though.