if you floor it quickly or relatively fast and the transmission kicks down than that sounds ok. if you gradually work the pedal to the floor it will most likely not kick down. it depends on the loud and speed. sounds like your carb. i had an auto 4 speed, (same gear ratio as yours just has overdrive) and it could pull any hill in my area in 3rd no problems. i just got a 87 with a g54b and will be swapping to the weber 32/36 dgv just to get rid of all the vacuum lines, might be what you need.