Why trans shifts hard 1-2 after battery went dead?

No check engine lights. Nothing was welded but the head had to be removed to drill out a broken manifold bolt.

Sorry got busy; Unless some thing got knocked loose, was hoping for a light. Was it jumped off or charged? Try taking battery cable off for a few minutes, make sure battery is charged, put cable back on, might have gotten a spike when charged. Leaving the shop, will check back in a bit.

I disconnected battery for a fe minutes and reconnected. It drives somewhat better initially but then the rough shifts returned after a few stop an goes. I read somewhere it might take 1-250miles for a transmission to relearn itself.

Haven't had a 4L60E have to relearn when battery was dead. There should be something else that has caused this situation. While checking the troubleshoot guide, was looking for a situation of your repair and what might have happened during the head R/R. The things that stuck out was the throttle position sensor, engine coolant temperature sensor, pressure control solenoid. Possible damage to connector, wiring, or bad connection, contamination, or ground wires bad connection, not reinstalled or broken from mounting connector. The other probable causes are mostly internal of transmission. Check the connections mentioned, if good have the transmission and ECM scanned by a TECH2 to make sure there is no codes, but also the vehicle can be driven watching scan data to observe the function of the fault with live data.