Recently I've had a drop in the volume of hot water that is coming through my system. It is a problem on every faucet in the house. The cold water pressure is GREAT. The house is 7 years old, and I believe that it has copper tubing throughout. I've been digging around for solutions to this for the last few days, and have tried several things.

First, I wanted to make sure that the water supply INTO the hot water heater was coming at good volume/pressure. I did this by opening the drain valve on the bottom of the water heater without shutting off the cold water inlet. There was amazing volume and pressure coming out of the drain valve, so I don't think it's the supply volume/pressure.
I then did what was suggested on numerous forums for similar problems. I shut off the cold water supply, opened the faucet that was the furthest away from the water heater, and drained the water heater. This was a slow process. It took about 2 hours for it to drain. There was barely any water coming out of the drain valve. Well, after it finished, I turned the supply water back on, filled the tank, and bled each faucet. At each faucet, the water looked sort of yellow at first, with one of the faucets (the first one I bled) it actually looked brown for a minute. The yellow color went away after a while, but the volume/pressure was still the same as before.
I looked online again, and a site suggested that flow problems could be due to the use of the wrong diameter pipe. I looked at the exposed piping in the basement which feeds most of the house, and it had an outside diameter of 7/8", so I assume that's 3/4" tubing.
I can't find any other ideas online, and this is really getting aggravating. We can't use the dishwasher because it doesn't get the dishes clean anymore. Showers have no flow of hot water, but at least there's something there.

Thanks for any ideas that you have. I really appreciate the input.