If it ran fine until you replaced the plugs, that would be the first thing to "double check"
1-are you certain all the wires are on the correct plugs?
2-Did you take care to remove the plug wires by (using special plug wire pliers) or pulling the connector itself, and NOT by pulling on the wire?
3-did you set the gap or check the gap before installing them?
4-did you drop any of the plugs before installing them?
Please don't be insulted by my questions. It isn't that I think you don't know how to change a few plugs. I'm just trying to make sure you didn't accidentally create a (miss or) problem without realizing it.