XNA 3D custom shader/effect gives shakey rendering in the distance

Question

I am rendering a simple flat plane + texture to use as the floor for a game. I'm rendering it using a custom effect I've written.

The problem I have is that the ground in the distance gets a bit distorted and shakey when the camera moves forwards and backwards.

If I render the same model + texture using the BasicEffect instead of a custom shader it appears smooth and works correctly.

Here's the XNA code setting up the custom effect:

Matrix worldMatrix = Matrix.CreateScale(0.2f);
_floorEffect.CurrentTechnique = _floorEffect.Techniques["Textured"];
_floorEffect.Parameters["World"].SetValue(worldMatrix);
_floorEffect.Parameters["ViewProjection"].SetValue(camera.view * camera.projection);

_floorEffect.Parameters["diffuseTexture"].SetValue(_diffuseTexture);

foreach (EffectPass pass in _floorEffect.CurrentTechnique.Passes)
{
     pass.Apply();
     device.DrawIndexedPrimitives(PrimitiveType.TriangleList, 0, 0, meshPart.NumVertices, meshPart.StartIndex, meshPart.PrimitiveCount);
}

Here's the shader code:

float4x4 World;
float4x4 ViewProjection;
Texture diffuseTexture;

sampler TextureSampler = sampler_state { texture = <diffuseTexture>; magfilter = LINEAR; minfilter = LINEAR; mipfilter=LINEAR; AddressU = wrap; AddressV = wrap;};


struct TexturedVertexToPixel
{
    float4 position : POSITION0;
    float2 textureCoords : TEXCOORD0;
};

TexturedVertexToPixel TextureVertextShader(float4 inPos : POSITION, float2 inTextureCoords : TEXCOORD0)
{
    TexturedVertexToPixel output;
    float4x4 preWorldViewProjection = mul (World, ViewProjection);
    output.position = mul(inPos, preWorldViewProjection);    
    output.textureCoords = inTextureCoords;

    return output;
}

float4 TexturePixelShader(TexturedVertexToPixel input) : COLOR0
{
    return tex2D(TextureSampler, input.textureCoords);
}

technique Textured
{
    pass Pass1
    {
        VertexShader = compile vs_2_0 TextureVertextShader();
        PixelShader = compile ps_2_0 TexturePixelShader();
    }
}

Videos to demonstrate what I mean:

Using the BasicEffect http://www.youtube.com/watch?v=matmrIZH-pU
Using the Custom Shader http://www.youtube.com/watch?v=Fu9P4D-UCTc (see it clearest in 1080p full screen)

Notice the difference when looking at the ground in the distance.

Answer 1

I managed to fix the issue by enabling the generation of MipMaps for the texture used by the model. This is done within visual studio by finding the texture in the content project right clicking going to properties and then expanding "Content Processors" and enabling the option "Generate MipMaps"