Had the same issue some time back. Checked oil level what seemed like almost 1000 times. Trans came out 3, yes three times. Pump seal was changed 3 times. Still leaked. We pulled the trans a 4th time & after many four letter words that begin with F, we discovered the circular weld on the converter hub (The one that drives the trans oil pump) was cracked!! Not visible, but showed up on a DyePen test. I hope this is not the case with your leak. Could be though, considering the trans is brand new.
For me always New Trans = New Converter.= Common sense.