You still have way too many islands. Get the total number of UV islands for the everything except the wheels down to no more than 3. Try to get it all into one big stretched out skin.
Download a trial version of Max 2015. Add an Unwrap UVW modifier to the model, hit the edit UV’s button. Select every surface on the body of the bus and then hit that button I showed you.
It will all end up as one island.
Also I looked closer at your topology there is a lot of wasted triangles on this model.
You can accomplish a 100% exact same shape by welding vertices and cuttinng the tricount down.
What jumped out at me was the roof. The rectangular space is split where the windows are. It should stay that way on your raw file
in case you want to change it later. But doesn’t need to remain split in the production version especially if it creates additional unnecessary faces
across the entire model.
And I think I saw some 5 sided nGons in your model. Looks like you have some in the top rear corner of the bus. Split those up into triangles or Quads.
If I bought an asset with nGons I would complain. It is just not professional to leave those things in. You should break it all up.
And if you don’t mind more critique. Post up a picture of your normal map also. I want to have a look.