Low Power and High Fuel Comsumption

Hi guys,

I'm getting about 30mpg and max speed is about 70 on the flat.  Foot buried, it sits at 70, I can get more downhill but I feel this is less power than  used to get. I've been driving a 1.0 corsa which feels like a rocket in comparison.

Does this sound normal or perhaps an issue?  I recently changed my thermostat as it was overcooling to about 70C, wouldnt get any higher.  It's not sitting at just below 90C once it warms up.

I'm thinking maybe carbon deposits have built up and blocked an injector or something?

Thanks in advance guys,

-Scott