It's in your rims. It's acting like wheel weights. You might have to take your wheels off to clean them, if you can't get at it from the outside.

caked mud on the wheels, or drive shafts, could create an imbalance that would cause shaking. Mud on the chassis or body wouldn't.

Or maybe you knocked off one of the balance weights.

Or you bent an axle

Probably still mud in the rims or maybe a balance weight came off.

Last night me and my bf went mud bogging in my car and now it shakes bad at like 60 but I got under the car and sprayed it with the water hose good to get all the mud out and it doesn't shake at 60 any more it shakes at 65 to 60 mph and I just got new tires and balanced on the car so is it mud caked up under the car that makes it shake?