1995 Mercury Cougar Car misfires around 1500-2000 RPMs.

Okay well the title pretty much sums it up. I was wondering if this could be a blown head gasket. This usually happenes when goosing the accelarator a little bit. As well a when the car reaches 30 mph and 50-60 mph. If this is a possiblity, ive looked online and found a TSB: 98-7-4 which is Engine gasket sealer. I only found it on a couple of 'unofficial' sites and not on the safecar. Gov.

Also, are there any other 'common' reasons for a car to misfire?

Thanks