Hi I have a 2000 mustang v6 that has a major vibration noticed it’s when I’m around 40 mph and around 1500 rpm and more. The vehicle was sitting for three years before I bought it the old owner said the put a new used engine in it that has around 80k. I had the engine mounts checked the wheels balanced, I’m still suspecting the u joints or the drive line but I’m stuck and don’t know if anything I’m overlooking of if anyone has had the problem and hopefully can help I have to take the car on a 425mile drive on the 7th of August so all suggestions will help

thank you for your time