In this code
you are getting the value from column 6, which is F. That's GVWR, not width. Then you get a value from column 13, which is M, which is blank.
You also seem to confusing the two worksheets in your code. Instead of activating a sheet, use explicit qualification for each cell reference.
Also, you are using a MATCH function to look up the position of the selected item, but the ListIndex property of the list already tells you that. ListIndex starts using 0 as the first item so you have to add 1 to get the row number. Also you have a header row, so you have to add 1 again.
You also use intermediate variables where they aren't really necessary. This sometimes make code more readable, but sometimes just makes it bigger.
You seem to be loading the second listbox from the list of trailer GVWR. I think you meant to use the trailer name.
One suggestion, which I didn't implement: You may want to create named ranges for the vehicle and trailer names. Then if you change the way your data is organized, you won't have to change the listbox range source.
Here is how I would write this code, book is also attached:
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