2005 Mercury Other

Transmission problem
2005 Other Mercury Models 6 cyl Automatic 62000 miles

I have a 2005 Mercury Montego, v-6 Automatic transmission. When I press the gas to speed up or try to go up hill, the r.P.M.'S jump up, I come to an almost complete stop, and it makes this horrible thumping noise. Any idea what could be causing this? Someone told me that it could be the valve cover. Please help!
August 29, 2008.

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