Don't just pull it all apart just yet..Do some more diagnosois..
Ok reverse is fine so you know the rear servo + direct clutch is ok.
1st works so the forward clutch is ok.
The only thing left is the intermediate band.Even if thats not working the trans will skip 2nd and go to 3rd.
Your best bet would be drop the valvebody + air test each component though each will be ok from my above comments on what does work.
Since the governor is ok i would be looking for a valvebody problem,maybe shift valves or check the actual modulator valve in the case is free..Even a new modulator should work ok as is ,the adjustment is more to fine tune.
I assume you do have good manifold vacuum at the modulator hose...