This is my son's Jeep so I don't drive it much. It is a 2010 Wrangler Sport with 130,000 miles. When I drive it like an old man, not jack rabbit starting or flooring it, it shifts perfectly. While going ~10 MPH in 1st, if I step on the gas hard, it thumps from the back while shifting. My son is in college now and I gave him my car to drive so I just noticed this. I checked the transmission fluid and it is fine. Does this sound like a lot of $$ to fix and is it worth it for a 2010 with 130K? My wife just says "why don't you keep driving it like an old man and you won't hear the clunk"?