TH 350 shifts

[cj847]

I am having issues with my 350 transmission (I think).

First - it pulls fine in every gear and has been modified by previous owner.
Shifts are extremely fast (chirps the tires shifting at light throttle) literally a split second vs the normal shift of a 350 trans where you can actually feel the loss of power during the shift.
Under mid/heavy throttle everything shifts perfect and the kickdown is adjusted just right.

My problem:
Under light throttle (like leaving a stop sign turning left - it will shift to 2 and 3 simultaneously under 15 mph. It's like driving a powerglide. I have good vacuum and the modulator valve holds vacuum.

Any ideas?