Hard Shift from 1st to 2nd

There is no adjustment on those at the carburetor end. The pre-74's had a slide at the carb end of the rod and a simple pivot at the trans end, but that changed in 1974 when they went from the Holley 1920 to the 1945. The '74's and later have the adjustment slider at the trans end. So, unless you got under there and fooled with it, nothing should have changed. There is a procedure outlined in the FSM that explains how to properly adjust the throttle rod, and nowhere does it say to "make sure the rod is all the way back".

Have you raised the idle so much that it's taking off in gear without you touching the accelerator? A closed-throttle upshift on a Torqueflite is quite noticeable. Why don't you set the idle back to the factory spec? That is 750 rpm, in neutral, warmed up with the choke off. You can buy used, old-style diagnostic meters from ebay cheap that let you properly read the idle speed. Also keep in mind that trans fluid on a Torqueflite is checked in Neutral with engine warmed up. Pump does not operate in park, you won't get the correct reading. Good luck.