IS THERE A DEVICE WHICH WILL ALLOW TRACKING ON A GPS UNIT?

You need a system to receive the GPS location of your trucks. Check with a 2-way radio dealer in your area. I used to install these systems when I worked for a radio shop. We set up several companies with GPS tracking for their vehicles.
Don’t expect real-time tracking like the special effects you see in the movies. It can be done but would be very expensive. Depending on your needs, you normally receive a vehicles location every 10 to 30 minutes. You can also poll a vehicle any time you want to see where it is if the system is between polls for that particular vehicle.

There is a gps device you can use to track a vehicle or anything else that moves or is likely to be moved or stolen. It uses Assisted Global Position System ( A-GPS ), which utilizes both satellite and cellular technologies.

Go here if you are interested in reading more about it: (click and paste into browser)

http://www.garminhandheldgpsstore.com/product_info.php?cPath=17&products_id=88

Go here for car installation kit:

http://www.garminhandheldgpsstore.com/product_info.php?cPath=17&products_id=89

I hope this helps.

garmin handheld gps

visit me at http://www.garminhandheldgpsstore.com