Any Idea why my car is stalling/losing power?

I recently bought a Suzuki Aerio SX and was aware that it suffers on steeper inclines, but lately it has been stalling on me. It seems to happen after I make a full stop, like at a red light, or when attempting to speed up after applying the break.
The car will just rev up like I'm in neutral and will shudder, before coming to a stop (the engine is still running). It can last just a few seconds up to a full minute or two before it gives me control again.
When traveling up hill, if it doesn't just stall, it will lose speed. Seriously, I can be overtaken by big rigs doing 30.
Any ideas?