727 shifts early

So my !969 Dart 340 GTS. 340 is running a solid cam. So far it looks like a 480 lift. Very low vacuum at idle. Like 6 inches. Running pretty good. Initial at 22 total 34.

What I notice is that even if I come off the line at WOT or WOT soon after the trans shifts out of first way too soon. Like maybe 20 MPH. Shifts out of second too soon as well. Like 50 tops. So my question is where do look? I have already adjusted the kickdown linkage as far as I dare go. Does not seem to have much effect. The kickdown is also non existent unless speed is very slow.

Ideas and thoughts? Oh and it is a 727.