C6 Super StreetFighter Woes

[TX69F100]

I have a brand new C6 SSF behind my 400ish HP 390 (1969 F100), and a couple of "funny" things are going on with it.

First, the 1/2 and the 3/4 shifts are happening WAY too soon. I read that the modulator valve can be adjusted to widen the shift pattern. Cranking in about 3 turns did not make a noticable difference, so I wanted to wait until I received professional advice before going any further, especially in light of the next issue.

Another thing that needs to be addressed is how the 2/3 shift is extremely firm even at part throttle, while the 1/2 shift seems "normal". Note that I do not yet have the kickdown linkage installed, as I need to replace the bushings in the ends of the kickdown lever. It was binding, so I left it off for now and have been shifting manually (especially since the auto shifts happen way too soon).

Please advise.

[TX69F100]

update:

Adjusting the modulator did actually widen the shift points. It needs a little more, but I think I'm good with that.

I still don't know why the 2/3 shift is so much firmer than the 1/2 shift.

Advice?

[TX69F100]

2nd update:

I've gotten the shift points pretty close to where I want them, now.

I still need to know how to correct the issue of the trans slamming 3rd violently even at part throttle.

Please help.