The 455 in a similar weight car should feel faster. There is a BIG drop from 1-2 gear in a 2004R. 1st is 2.74 but second is 1.57. If the transmission isn't holding first very long, it's going to bog if it goes into 2nd too early. If the engine tuning is way off, it's not going to come up on the converter properly as you mash the gas. That's why we keep asking if it will turn the tires over from a stop.
Since you're new to Pontiac, you may not realize what you've got. A drivetrain like yours should blow the tires off from a stop. 2-1 downshifts at 20 MPH should break the tires loose. It should scare you a little. The fact that it doesn't points to something seriously off. I bet it's a combination of timing, carb tuning, camshaft installation and transmission settings. Timing just a few degrees off will have a huge impact on idle quality and throttle response.. Having the Q-jet carb secondary air door open too fast will produce a huge bog when going to WOT. Little things make a big difference.
Some light reading on 455s and cam selection:
https://forums.maxperformanceinc.com...=550405&page=2