Hi Dan,
Same rear gears, so probably just as slow.
I'm building a '55 1st GMC 1-ton as a driver/trailer puller. I replaced the rear with a GM 14-bolt with 3.42 gears and I'm putting a Cadillac 500 in mine so speed won't be a problem.
I'm swapping the IFS crossmember from a 70's 3/4-ton under mine to provide disk brakes and power steering.