Suv shakes when I apply the brakes

I have a 1991 ford explorer, when Im driving on the highway around 60 to 70 mph the truck shakes lightly but when I get off the highway on an offramp and apply the brakes the truck shakes vigoursly to the extent to were you would think something would brake, I have replaced numours parts trying to fix this problem here is a list of them, new brake pads, new brake rotors, new brake shoes, I checked the rear axel's with a dial indicator, one of them was bent, replaced it, replaced outer tire rod do to it being worn, new shocks, when I have the front end of the truck jacked off the gound and I move the steering wheel there seems to be a slight slack in the steering, could this be why it is shaking, also to mention the truck was fliped when we bought it at 30,000 miles, but it didn't start shaking till about 85,000 miles, can you please help me?