Randy,
You were very right to switch to tables in one file. That is always the best way to do a simple setup like this.
Now, to be able to help with the best method for your system, we'll need a little more information.
1. Roughly how many trucks, drivers and trailers do you have to work with?
2. how often do trucks change trailers and drivers change trucks.
3. Is it safe to assume that the truck is connected to the trailer and the truck to a driver? (obviously from a Database perspective, I understand that a driver needs a truck to pull the trailer)
4. How many different people are going to be using this program, just you or more?
Sorry to respond with questions, but for a best case, they really do matter. Hopefully with that, someone else may chime it.