According to this:
DeLorme Street Atlas USA File Types
you should be able to "play" the file back directly from within the delorme program.
Here's what I found when I searched .gpl within delorme itself:
Quote:
Playing Back a Log File
After you log a route with your GPS receiver, you can play it back in the mapping application and review your entire journey on-screen.
Your log will play back in NavMode unless you have it turned off. For more information, see Using NavMode or GPS Tab View.
Notes
You cannot play back a log file if you are currently tracking with a GPS receiver.
Zooming in on the map allows you to see the log file in greater detail.
When you play back a log file in NavMode, the tab area is not minimized; this allows you to control the playback.
To Play Back a Log File
Use the following steps to play back and review a log file.
Click the GPS tab and then click the GPS Log subtab.
Click Clear Trail to clear any existing GPS points from the map display.
Click File and then click Open.
Single click the file you want to view.
The bottom of the Open a GPL File dialog box opens the start location, start time, start coordinate, total distance, duration, finish location, finish time, finish coordinate, and the number of readings for the selected log. Log files have .gpl extensions and are saved by default in the C:\DeLorme Docs\GPSLogs directory.
Click Open.
Click the Play button to begin playing back your log.
OR
Drag the slider in the Progress Bar (see graphic at the end of this topic) to the point in the log you want to play.
Note Playing back a log file defaults to 1x, which occurs in real time and takes the same amount of time as the original trip did; for example, if your trip took six hours, the on-screen tracking process also takes six hours.
You can also:
From the Playback Speed drop-down list, select an option (2x, 5x, 10x, 25x, or 50x) to increase the tracking speed accordingly.
Click the Pause button to pause the tracking of the log file. The Pause button turns blue to indicate the file is paused. Click the Play button to continue playing back the file.
Click the Stop button to stop the play back. To start the file over, click the Play button again.
Click and hold the Rewind button to rewind the log file to a particular point.
Click and hold the Forward button to fast forward the log file to a particular point.
Drag the slider in the Progress Bar to view a particular point in the log. You can drag the slider forward or backward.
This is from Street Atlas 2009 plus.