Brandon,
There could be several reasons for this problem:
# Make sure tires are properly inflated all the way around
# Wheel Bearings
# Tie Rods Ends
# Ball Joints
# Braking System ex. (Rotors, Brakes, Calipers, etc.)
# Or could it be an engine issue at higher speeds as if the engine isn’t getting the proper ventilation/oxygen it needs to correctly run? Spark plugs, fuel filter, air filter
Hopefully, this gives you some ideas as of where to check next. I am no master mechanic but I can tell you from the problems I have had related to this have almost always been engine or braking system related.