904 Kickdown issues

I just recently did a /6 to 318 swap in my Dart.

I installed a used 904 that a nice fellow in Denver let me have for free. All I did to it was install new front and rear seals, selector shaft seal, and new filter and pan gasket.

The tranny is from a mid 70's scamp, and its working great in the dart except for one small issue. This trans seems to have the part throttle kickdown feature, which works great,,, if i'm cruising through town,,,30-35mph in high gear, give it a little gas and it kicks downshifts to 2nd, no problem.

However if I'm going like 40mph or above, the tranny wont shift down when I step on it, even if I floor it.

My first initial adjustment of the kickdown linkage was to prop the throttle all the way open, then crawl under and move the lever on the trans all the way back, then tighten down the clamp.

Do I need to play with the adjustment a little more, or is there some other issue with this trans ?

P.S. Car is 68 Dart, 318-4bbl, 904 auto with 3:23 gears in back.