""this might be too simple but would a weaker spring on the 1-2 shift valve let it move (shift) earlier and a stouter spring on the 2-3 shift valve so it would shift later. No expertise here just thinking out loud""

I tested with a couple different governor assemblies until I got my 1/2 & 2/3 WOT shifts in the "range" that I wanted. Then I started testing with different shift valve springs to dial in each rpm.
Since the diameter of both valves are different, they react different when changing the fluid pressure. My goal was to get my 1/2 and my 2/3 WOT shifts to be the same rpm. When I started, one was 400rpms different than the other with the stock springs. I found that dialing in the spring pressures was an easy way to tweak one or the other to bring the WOT shift points closer to each other. Now both of these WOT shift points appear to be the same on my tach (non digital). It should stay that way as long as I don't adjust the line pressure.

Note: I pulled the spring out of each valve hole. I used a digital scale and pressed each spring against the digital scale to just under coil bind. I wrote down what each spring showed on the scale and then got online and found a couple of spring manufacturers and bought springs with the same OD, but different spring rates (it was a guess, so I picked a few). Then once they were shipped to me I used the same digital scale and wrote down the readings (lbs @ just under coil bind) of each spring and placed them in their own plastic baggie. Then I just swapped in springs based on if I needed more or less spring pressure until I got my shifts where I wanted them. I found that the two spring companies that I used wanted me to buy a minimum of 2 springs of each size. I don't recall exactly, but I might have bought $10-12$ worth of springs plus shipping per each of the two companies.

Note 2: Before I bought the springs, I bought the Split Shift spring kit from A&A. This kit got me to within 200rpm between the two shifts. I wanted the shifts to be even closer together, so I bought the springs for testing. This is also when I bought the re-usable transmission pan gasket which worked out great when I had to pull the pan 4-5 times to get the springs correct.

Note 3: I found that the heavier shift valve springs delayed the WOT shifts as noted above. I also found that they delayed the light throttle shift points too when the tranny is in D.