TT Newbie - Need Help

I am considering purchasing a Prime Time Tracer 3150BHD TT for me and my family. However, the near-term use is to provide a temporary home for me and my family 4 hours away (~250 miles) while I undergo a double-lung transplant. The 3150BHD has a dry weight of 7000 lbs. and I currently have a 2005 F150 4x2 with a 145" WB, 5.4L V8, 3.55 GR, and tow package and the big whamy, 170,000 miles. This truck is rated for a max. TT weight of 8600 lbs. and a GCWR = 14,000.

I have never pulled anything this heavy, but with the truck having so many miles I am a bit nervous about purchasing the TT. I have read many forums and have noticed that most folks who have similar vehicles recommend not towing more than 6500 lbs. packed. I have researched TT after TT and have not found many under 6500 lbs. that will serve my purpose. I need length so that I can sleep 6-8 people but I want to keep the weight as light as possible. The drive to my locations is primrily flat with hills and so it is not driving in the mountains by any means.

So, my question. Do you experts think that I should forgo the TT due to the age of my truck. BTW, I cannot afford to get a TT and a new truck so I have to rely on the one I have.

I would greatly appreciate any help with this as I need to decide whether to purchase the TT or not.