There should be a couple types of adjustments on the carb, or down near what is called the 'kickdown lever' at the front of the trans. Drivers side. You should be able to see it following the linkage down on the drivers side. basically, the more that lever gets pushed back, the longer time between shifts, and also changes the 'kickdown' of gears when you step on it (atleast on later models with the part-throttle kickdown). Anyway, what you need to do takes a bit of test n tune to get it how you like it.
You need to get that lever to go back further compared to how you have it now when you give it gas. You can kinda tinker with it from there. However make sure it doesn't interfere with full throttle. At full throttle that lever should still move about 1/8" if you push it back by hand. That is so that the lever doesnt bottom out and hinder your carb from getting full throttle.
Hope it helps.
-Mike