Just posting for those who may have experienced a similar issue.
Our Impala developed intermittent transmission issues on take off about 3 years back. Ultimately it required a rebuild as evidenced by the chunks of metal found in the pan.
After the rebuild all seemed good, but the even more erratically intermittent pull off from a dead stop plagued us. Numerous checks by my transmission shop never found a cause except they finally said it MAY be the tcm. I kept driving it and living with the issue while keeping an observant eye on anything that might indicate a decline of any kind. During and before this period and before we also had fuel pump issues and replaced it twice. A little over a month ago the fuel pump failed again. Aggravated, I simply parked it and was about ready to sell it cheap. While parked it might crank and run and it might not and there was not observable pattern to when it might decide to run. Finally decided to do some troubleshooting 101 and when to check the fuel pump relay....I immediately spotted a fuse that was darkened on one side. Further inspection proved it was not blown BUT...on blade was obviously not in good shape as the result of a loose connect to the fuse box. Cleaned things up, installed a new fuse with a coating of Oxguard on each leg and bingo! Fuel pump issue fixed.
now the REAL quirk. After all this time living with our erratic transmission this repair has corrected that issue as well!!! I'd sure like to hear from someone in the know that can explain how a power issue to the fuel pump corrected a transmission issue as well. My only thought is the inconsistent power voltages to the fuel pump was being sensed by the ecm and tcm thereby affecting the electronic orders being sent to the transmission.
I find the entire scenario interesting and eye opening. I feel there is a strong likelyhood one or both fuel pump replacements were potentially unnecessary and due to the intermittent nature of the voltage failures showed the pump as receiving power during troubleshooting. Everything pointed to failing fuel pumps and both replacements gave most of a year of service before the symptom recurred possibly because a fresh fuel pump draws slightly lighter amp demands thus allowing the lower amperage need to pass through the weak fuse connector until age or condition increased the demand and causing the arcing and connection overheating I found evidenced on the fuse.
Mainly posting for anyone else who has or is experiencing a similar gremlin to save them some of the head scratching I experienced.