I was getting about 240 miles to the tank of gas and now I am only getting about 180, any possible causes for this?

I just changed all the fluids. My last tank took me 475km.
Couple weeks back we were only getting around 400km.
I was noticing that when I let off the gas it started to slow down, like a dragging feeling. Now it feels great and has more pep. Uphill in 5th and going.

Can't remember if you said you did all the fluids or not.

When was the last time you changed the fuel filter? It might be a good time to do this. Also, when was the last time you changed your spark plugs. It might be a good time to do this too. While you are at it, you will want to do a pressure test on each cylinder. I just did mine and I have a leak in #1 and #2. I think the head gasket has broken between each and they are cross feeding each other pressure and allowing it to leak past the open valves in the adjacent cylinder. I'm getting similar gas mileage in my Sportage as you and mine dropped suddenly as well. I also have almost no power when going up hills. I have to drop all the way to 3rd gear and the max it will get up to when going up a medium hill is 35 mph with the gas pedal pushed to the floor.

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I just replaced the fuel filter just a couple of weeks ago. The spark plug I changed out in november, but I have 9000 miles on them now. When you say all the fluids, what all are you talking about? Tranny and t-case included? I am having the same problem when going up hills. I might be able to get up the medium hill at 40 mph.

Yes. The fluids I changed were the Manual Transmission, Transfer Case, Front & Rear Diffs.

There is this long hill where I used to live in North Vancouver called The Cut. It is a good hill, has length and height. When we first got the Sporty we could get up it in 4th, as long as we hit it in 4th at about 4grand. This slowly over time got worse. No matter how fast I hit the bottom of the hill I would always end up in 3rd by 3/4's up. Last week I was coming up to this hill and the car in front of me was going way slow, Change Lanes Man!...lol..anyhow, after I got around him I was going up and I shifted to 4th and it was speeding up! I actually shifted into 5th going up the hill about 2/3's up.
It is my belief that the Sporty didn't like that thick old oil. Has way more pep than before.
I have not changed my fuel filter yet. Great....now that I have said it..lol..So where is it and how fun is it to do?

Remove the battery and the battery box stand, you can see the filter down there. The hard part is getting the lines to disconnect, A screwdriver helped me.Putting them back on was a breeze. remember to relieve the fuel pressure first. Take the gas cap off.
I going to go and change all my fluids. Maybe that will help.

If you can go all Synthetic do it.
I would have but was a little steep. I did get Synthetic for the engine though.
From what I gather, I don't believe it would be a great idea on high mileage vehicles.
I only say this as I was asked the mileage on mine when I switched over.
I am at about 160,000 I believe...I should look. I always have it on how far did one tank get me setting.

I have about 121k on mine. I have noticed a small oil leak bown below. The underside of the tranny has oil on it. I am trhinking about just changing out everything for the clutch and while I got it apart, do the rear main seal. I also think I have a small leak up the the valve cover back by #4 cyl. Would an oil leak cause lack of power and lost milage?

do you mean oil in the plug hole in number 4 cyl ? if so pull that plug and see if is is oil soaked if so clean out the hole change clean the plug or change them out replace the valve cover gasket. you might only be running on 3 cyl's

no there is no oil in the hole, just on top. the top of the plug is covered but when I take the plug out the part that is inside is nice and clean, just normal stuff on the plug.