Lacks power I had my alternator replaced 2 weeks ago, and now my explorer is spitting and sputtering at me, as if it were cold out. Check engine light flashes at me whe nI try to "kick it down" a little bit, but this light has been on since I bought it 2 yrs ago. Never any problems til the alt. was replaced. I had plugs/wires replaced in feb of 08 along with new fuel pump and filter also

I suspect that something has caused a short of one of the diodes in your alternator and the alternator is only putting out 1/3 of the current it should. Maybe even 2 diodes are out. Have the alternator checked.

It may have fouled your plugs, but you can tke them out and clean them. Use a small blade and scrape the carbon off.
You could also take the egr valve off and try to clean it. Use a wire brush. also clean as best you can the passages under the valve, they can get plugged with carbon. Use a new gasket when you bolt the egr valve back down. Keep trying to get the fuel filter off, but the egr cleaning should help.

If the check engine light is not on, I doubt there is much you can do.
It sounds like one of the engine temp sensors or one of the other sensors. The engine temp sensor and the intake air temp sensor tell the computer what the outside air temp is and the coolant temp which allows the computer to regulate the amount of fuel going thru the injectors. Generally if one of the sensors has failed the check engine light should be on.
It could be low fuel pressure too.
You may have to have a shop check the sensors with a scanner and the fuel pressure with a gauge.

You need to check the out put of the alternator. In general the alternator should put out 13.5 to 14.5 volts. I would say go to where you bought the alternator and have them check the voltage. If check engine light is on you should have a code get them to check the code. Most auto part stores where I live will check your code for free.

It certainly won't hurt. Also, check the timing.

Could be a clogged fuel filter, and or dirty fuel injectors. Try running some strong injector cleaner through it. It may take 2 or 3 times before it cleans the injectors out fully.

i would take it back. they should cover it. sounds like mass air flow sensor. if it was barelly detailed it water might of seeped into the intake thus sucking small amount of water which then causes sputtering and a little lack of power.

run scanner for trouble codes, some auto parts store will do this for free, check starter solenoid, check voltage at battery , 12+volts not started ,  14+ amps when running 

you may have gotten water in your gas it happens alot

You need to check a service manual on this but it sounds a bunch like a cold-start valve isn't closing once the engine is warm and this would cause an overly rich fuel-air mix that would gag a warm engine. I don't know if your car is equipped with  one or not.