Try adding a cam. Check out www.camhelp.com
and see what can find. Don't go wild! Find your particular engine size and and year. All 86' and up small blocks I believe are equipped with hydraulic roller cams. Find one with good low RPM to mid RPM power. You won't need much on the top end. Could also try some lower gears. Most trucks came with 3.42's and lower in numerical order. Try 3.73's if you have a 700-R4 tranny.
You might also try www.sdpc2000.com
and find a GM cam. These are a great alternative to pricey aftermarket cams. If you do decide to install a cam, besure to follow the rocker arm adjustments and cam breakin procedures properly. Hope this helps out.