You're pressing the brake. Or...you aren't pressing the gas all the way. Or...you can't drive. Or...you work for Polaris. Or...you can't expect a SxS to climb hills.
These are all the things I was told when I started complaining about this way back in December of 2013 when I took delivery of mine.
Certainly, verify that the machine is healthy...but I think you'll find this is pretty normal for the 700. As @snuffnwhisky pointed out, it's a altitude power loss/gearing combo thing. Down near the surface of the earth, it runs well enough to get the job done, but up in that thin air it can really struggle.
Are you willing to do a pipe? Don't know how much it would help...but I suspect a lot.
Some things you can do to a realitively stock machine:
Remove the air box lid if your riding allows it. A UNI or k&n will help. Anything to open the air box up...like a second air inlet? An exhaust tip from eBay does help a touch, without too much more noise. The intake boot had a big lip just before the throttle body that has to add a restriction. Remove it with a Dremel. Run the thinnest oil you can (this is about converter stall speed more than friction).
I don't know if a power commander allows you to modify timing on the 700, but that's an area where I think there could be gains, as these engines are about as highly tuned as a lawnmower.
And on the more wild side, a guy here built a turbo charged 700 (@spifyd).
The real question is why fight the battle when you can just trade it for a 1000 and cure it all? Legit question...