Car feels like getting kick in butt

hey i have a 03 caravan and when driving at hwy speeds it feels like the car is getting kicked in the butt or like it is getting held back. it does shift throug all gears just fine but just gets this thump feeling when going at 60-65. fuel pump and filter changed about 2 months ago and transmission level is good.

Tire problem??/ Thump thump thump sound as the tires rotate?

not really like a thump from a tire but rather like your driving along everything is good and you feel a thud. like a hesitation in the momentum of the car. almost feels as if you were hit in the back end of the car just not that hard