If it pulled hard in 1st and 2nd all the way to 6500 and then nosed over in 3rd I wonder if you may have a fuel delivery problem. What sort of fuel pump do you have? And what size fuel line are you running from the tank? Also if you are turning 6500 at only 101 mph you are either running a very short tire, or the converter is slipping. With a similar set up in a 63 Nova, with 5.13 gears and a 28 inch tire I was running through the traps at 110-111 mph turning 6500.

Pat