Head Gasket?

As I was going home one day as I hit the gas the whole car started to shake and rattle. I have been driving like this for about 4 weeks now and I have noticed that I have been getting very bad gas mileage. I have heard these 3.8L engines have problems with the head gaskets and I was wondering if this was it. It has not started to smoke out the tail pipe yet but the rattling is getting worse by the day.

I'm not a machanic but this sounds more like a vacuum hose problem...I know a broken or leaking vac. hose can cause simular problems.....If you had a head gasket leaking, there would be other indications..like water in the oil....or overheating with a bubbling in the radiator due to compression leak in the water jacket...good luck!