You have a problem somewhere, either converter is broke (my guess is sprag) or the dyno you used is about 200hp off.
@ 3300lb a 1000hp motor should run at worst 6.0's if all else is correct.
A good friend of mine has a 1025hp motor in his 3200lb 55 chevy it runs 5.8's all day.
Tell us more about your setup maybe we can figure something else out.