OK, did I mess up?? I just did a GRAVE DIGGER truck for my grandson's birthday. It's not really a "copyright" but it is a "trademark". Are the rules the same as far as using it?

The rules are the same, but i'm assuming since it's for your Grandson that you are not charging for it. So as long as you don't receive any compensation for it you'll be ok

Copyright refer to concrete works for example:
literary works - textual material, computer programs, compilations
artistic works
dramatic works
musical works [the music itself, and the sound recordings]
cinematograph films
broadcasts
published editions as typographical arrangements

A trade mark can be a word, phrase, letter, number, sound, smell, shape, logo, picture, aspect of packaging or a combination of these.It is used to distinguish the goods and services of one trader from those of another.

Very simplistically, the name "Barbie" is the trademark while the distinctive doll is copyright.