my 89 318 TBI is pretty good. It's got steep gears (390s?) and the 3 speed TF.
The motor and computer is pretty well set. You have to tune for best performance with what you have. Make sure the injectors are nice and clean, along with the intake and valves. Try Techron and/or Seafoam. Change the oils out for synthetics, and pump up the tires.
One thing that could help and would probably not be seen by the computer would be a steeper gear and a 518 trans with add-on switches. Adding a 4th gear and maybe a lockup should get you more off the line power and better freeway manners and MPG. Should fit, they came in later vans.