Sounds like to me it is spinning badly. I run 104-107MPH and run 6.30-6.50's with 60' down in the 1.30's..(But I have a big stall 6000)
Still I think you are having either traction issue's or suspension issue's?..
If it was the converter I would think the MPH wouldn't be there.
What suspension do you have in the rear? Also 3400Lbs is heavy for a glide.. Also with track prep that few and far between I can see major traction issue's..Go to another track and see what it does there..