PHP Hydra - google is your friend. Buy one from the vendor of your choice, download PHP software to PC or laptop (not Mac), connect chip to computer with cable, pull pcm from truck to get pcm code from paper sticker label, select desired tunes from PHP library that are appropriate for your PCM, install tunes on chip, clean the terminals on PCM as instructed, install chip on PCM, reinstall PCM, and drive away happy.
The PHP tuning is regarded as "better" than some of the more generic tuning from superchips etc. By "better", they mean better suited to your particular year and configuration (manual/auto), where others are more broad-brush.
7.3 and 6.0 both were available in 2003.