We have a 2004 Mitsubishi Endeavor AWD and it seems that the AWD is not working right.Rain, snow, bumps will make the car slide sideways. This happens with the front or rear tires.We took our Endeavor to a Mitsubishi Dealer and the first thing that they said is it has to be the tires. We just replaced the tires last week with new ones. Need alittle help with this one.

I am not familiar with that modle, but generally i would raise the car and support it securly.
Then if there wasn't a drain plug, i would remove the pan from the transmission ,following instructions from a good service manual.
hope this helps

The rear suspension bushings are worn out. Same thing happened tio mine. Wears tires out fast too.

COULD BE YOUR CV JOINTS. TIRE GUY SHOULD HAVE SPOTTED. CHECK THE RUBBER BOOTS JUST BEHIND THE HUBS. CRACKED? TAKE TO DEALER

check your sruts

Full capacity is:

FWD - 8.9 quarts
AWD - 9.3 quarts

Just a drain and fill is usually between 3 and 4 quarts.

Recommended fluid is Diamond ATF SP III

Fix your car right away by clicking the link I attached https://www.reliable-store.com/products/2004-mitsubishi-endeavor-xls-awd-workshop-service-repair-manual

No it's just is hard to pull out; be sure you place the new filter in with the arrows facing the engine intake this assures that you did not put it in upsidedown

It's probably not that the wheels are moving at a different speed. It sounds like a simple alignment issue to me. Installing a bearing could have thrown it off. You should just have a simple alignment job done.

The front three should be easy enough. They are right in front of the intake plenum. (big black plastic looking thing on top of the engine. The back three are underneath the intake plenum. It seems like a lot to tackle but it is really not that bad.
As always, if you are not sure you have the skills to attempt this go to a qualified mechanic. I did mine in an afternoon.