I tow with a expedition with the "camper" tow package. The gross tow rate is 8900 lbs. My current TT has a gross weight of 6800 and it tows ok. I have made several trips, and leaving this weekend for another trip into the mountains. Last trip I followed my brother who tows with a GMC 2500 diesel and I had no problems keeping up. Would a truck with a longer wheel base tow better - probably. If you plan to use the Expy, I would look at switching to heavy duty truck tires. They do effect the normal ride but they tow much better.
Several years ago, I had an F-150 with the 4.6 engine. It would barely tow my bass boat. Personally, I would not want to tow with that engine even on flat roads, so yes, I think a replacement would be in your future if you plan to tow with a truck. JMHO