http://cfmoto-forum.com/800ex800/question-about-stock-tires-zforce-800-53/msg2188/#msg2188
I did a search on this forum and found an answer to the exact same issue I've had with my SXS since new. I also thought that the tires just had flat spots from sitting on the showroom floor for who knows how long. But after two tanks of gas it has not gone away. So I will be taking it back to my dealer to see what can be done. So far I am not impressed with this machine.

As for the original problem of this post. I took it in to the dealer for that, of course they couldn't find anything wrong with the machine or the gas that was supposedly the problem. I got it back from them and other then adding a can of fuel supplement, and nothing else, it's been running fine, except for a very slight hesitation off idle and it doesn't seem to have the power it had before. So I will be asking about this when I take it in for the tires. I'll try to keep you all updated as I'm sure you are all sitting on pins and needles, waiting to see if these issues get resolved! 

One more thought, if you were running a very high RPM for an extented period of time this MAY also cause this power loss to occur.  Did this happen by chance?

What is considered "very high RPM"? The trail we were on was straight and smooth, but there are stop signs every couple of miles. We were going about 40 MPH not sure what that translates to RPM. The temp gauge was only about a 3rd of the way up from cold.

I've had the same problem, twice.  My shop test drove it and it threw a EFI code, so they replaced the speed sensor.  Yesterday, on a 53 mile ride I had no issues at all.  One thing that I would ask is, were you, by chance, in 4X4 high and running fast, like 25-35 mph?  I don't know if there is actually a "limp mode" built into these machines, somehow, so this is only a theory.  The second time this happened to me I may have been in 4X4 running fast.  I limped off the trail and idled.  A Jeeper cam along and offered to tow me back into Yuma, but he wanted me to try sometime first.  He had me shut the engine off, wait a minute, or so, and then turn on the fuel pump until it stopped.  Turn it off and cycle the fuel pump again.  He had me do this three times.  Then, he had me re-start my engine and, for whatever reason, all of my power was back.  I drove fairly slow back, so no power shut down.  Honestly, I think my 4X4 high switch was on when this power loss happened to me.  Please reply about 4X4, because I really need the satisifaction of knowing.  This power loss bothers me because I have no solid answer(s) to it.

It was in 2WD all day.

Hi, I'm new here and to side X sides. I bought the aforementioned in the subject line, off of the showroom floor. I have put 200 miles on it and on the way back to load it on the trailer and head home, it started running like crap and could only go about 15 mph at the most. If I pushed the throttle little more than off idle it would just bog. With about 20 miles to get back to my truck, it was a long ride to say the least. What would cause this? Thanks for any help on this.