and get a tonneau if you don't have...
Extang 2560: Black Max Tonneau Cover S10/S15 1994-2003, 6" short bed Isuzu Hombre | JEGS
and an extruded tailgate lip will help a bit too
Chevy S10 1994-2003 Wingswest Urethane 3 pc rear tailgate spoiler No light | eBay
...except that one's too big but you get the idea. You wanna trip the air to slow it down before separation.
You will know when you drive in the rain/snow and you notice how much wake is behind you. You'll be slicing through the air.