Recently got a new road bike, however while on a particularily arduous hill last week; the back wheel stopped responding to the pedals going forward.

Gear shifting works, pedals turn the back gears.. but the wheel doesn't go with them. Everynow and then it feels like the pedals/chain "Grabs" the rear wheel and it works normally until the next bit of tension and then continues not to respond.

I've taken the wheel off, tightened the bolts, loosened the bolts in case too tight, but still at a loss. The chain is sitting on the gears nicely, but still no luck.

Thoughts?