I assume you've played with the starting line chip to try hitting the converter harder, some where around 4200/4400 on the brake. I think you're right it should go in the 1.40's. Do you have a set of 4.86 gears? also you can back the cam down to 100/102 installed for more torque on the bottom end. My friend Jimmy Smith does this with his 3100 lb Camero with 358" engine and runs 1.47/1.49 60' times, but he also has a 5500 stall converter.
Just a guess
Zip.