With an automatic transmission, the torque converter must be locked when pulling hard or the transmission will get hot quickly. The 68RFE does not lock the torque converter in first gear in stock configuration, and by the OP shifting back and forth between 2nd and third, he didn't give it a chance to lock up in second gear. A lot of people post about overheating their transmissions while backing their trailers or pulling hard at low speeds. It's because the torque converter is unlocked and creating huge amounts of heat in the process. An aftermarket transmission controller would be a big help in this case, enabling the driver to lock the torque converter at low speeds, helping keep the transmission temps in check.
Rich
