My 2003 Hyundai Accent GL died randomly while driving on the freeway... Why?

So yesterday, I went to Pep Boys and purchased 4 new tires, got a tune-up, oil change, and fuel injection service. 2 weeks ago I had battery problems, checked with Auto Zone, they said alternator is fine but need a new battery. Bought the battery and new connectors that go from the wire and attach directly to the battery. I had the mechanics check my belts because they squeal frequently when first starting the car. Said that they look fine without damage, though i should replace them since I've had the car for 4 years. I didn't have the money so i didn't do that. I was also told that i need to replace my CV-Axel and two parts related to the "boot" on the front drivers side tire. well that's about another $500 so i didn't do that.

What could the problem be?? Any ideas?

Thanks.

Clean your throttle body. Your butterfly/ silver blade is sticking.
http://www.mobiloil.com/USA-English/MotorOil/Car_Care/DIY/Cleaning_Engine_Throttle_Bodies.aspx
Franco