Does the shaking span a 10-15 mph of when it starts and stops?
If so you have a broken cord in a steer tire, if you have a jack heavy enough to lift front end jack it up enough to get front wheels off the ground and see which one rolls on it's own.
That is a very common problem with 22.5 tires, if you end up needing new steer tires go with a load range h its a 16 ply tire and I bet yours are load g 14 ply.
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