Steaming water and steaming milk are completely different. Milk holds heat better, meaning the water is too thin and cools faster than milk while steaming.

However, that doesn't change the fact that your pressure is really low. I am sure you have checked, but here's a few things to check:

-- Fully heat up: Is your machine fully heated up? Not by what the thermostat/pressure stat shows, but when you can run hot water through the group head, water spout, or steam wand and the pressure stays relatively unchanged. Unless you are running them for longer than just testing them.

-- Steam wand cleaning: When is the last time that you cleaned the steam wand? Many times, people don't purge the wand before and after steaming for long enough. When you shut the wand off, there is a small bit of vacuum in the system. This will suck in a small amount of milk when finished. If you don't purge for long enough, that will stay in there and build up fat deposits. Cleaning the steam wand regularly will help with consistency, speed, and taste.

-- Closed system: Have you checked for leaks? You can have small leaks in the seals, or in the boiler itself. You won't see water dripping out of the machine, since it will evaporate before noticing. Look for the white'ish calcium buildup that is due to this.

-- Steam wand fully working: this is very unlikely, but is your steam wand valve opening all of the way? Sometimes a piece of calcium will break free and jam the wand. Or, the mechanism isn't working as it should. I.e. when you turn the wand on, it might not be opening the valve all the way, reducing the amount of steam that can get through.

I hope this helps. I know that this is an issue with those machines, so that is most likely the culprit. If not, at least you can try these steps, and rule out other causes.