A904: 1-2 shift happens early despite governor weight- any way to adjust this?

You have to change the 1-2 shift spring in the valve body. In addition to the governor weight, which it sounds like you have already changed, you sometimes have to put in a heavier 1-2 shift spring to make both shift points match. A&A transmission sells them, they are cheap. You will have to pull the valve body to change it.

As it is, your wide open throttle shift points should be higher, nearer 5800 as that is the weight you put in. Make absolutely sure that your tv (throttle valve, kickdown) linkage is properly adjusted, all the way back at WOT and all the way forward at idle. By this i mean the actual lever on the trans.