running out of breath in the 1/4 mile

hey guys
yesterday I got to take my duster to the strip for the first time
drove the car out there (about an hours drive) made a few passes and drove her back home

altogether, I'm pleased but I did have an issue making the actually passes

about the time the car hit 3rd gear (727 auto) she would stumble and fall on her face, the after a little while she would recover again

time slip is pretty telling, especially if you compare the 1/8 MPH to the 1/4 MPH

My best slip looked like this
Reaction -.0365
60 ft. 1.9853
330 f . 5.5913
1/8 et 8.7194
1/8 MPH 74.78
1000 et 11.8284
1000 MPH 72.96
1/4 et 14.9149
1/4 MPH 71.88

I actually lost 2 MPH between the 1/8 and the 1/4

the car is a 71 duster, with a MRL build 408, dynoed at 423 HP and 470 foot pounds
Comp Cams XE268H cam with a preform 750 (holley style carb)
I'm running a stock mechanical fuel pump, with a steel line (whatever stock size is, 3/8th maybe?) and a steel fuel filter going into a braided line to the carb

it looks like I'm emptying the bowls quicker then I can refill them
would this be a float issue, a bottle neck between the pump and the carb or do you guys think the fuel pump is just not up to the job?