My central air had been working fine. We have in the last 2 weeks had temps of 95 with heat index of 115. All of a sudden yesterday my air coming out of my vents was not as strong. Its cold but real slow. We changed the filter about 3 weeks ago, I went out to the unit and it was running. Any clue? Thanks.

Recheck your filter and make sure it didn't get sucked into the fan.
Secondly, look for any ice on the larger line exiting the indoor coil. Or if you can see the coil look for ice build up. Ice build up could be caused by a few things.
1. Dirty or plugged indoor coil.
2. Low refrigerant charge do to a leak.
3. Indoor fan motor beginning to fail.
4. Make sure nothing is blocking any of you cold air returns to the furnace.

This is where I would start.