Probably has the same delayed PE that the later LQ4 6.0s and 8.1s do.
Explains why the 454 I towed with years ago felt gutless compared to the way my L31 ran when it had the milled 906s with 2.02/1.60 valves, 395 cam, marine intake and thorley tri-ys. I did 303 tq @ 3,400 (290@ 2,900 where the pull started) and 230 hp @ 4,400 with bad valve springs. Swapped the springs and retainers to LS6/Comp787 and put down 310 tq @ 3,200 and 257 hp @ 4,800. Those were locked converter 2nd gear pulls through a 4L85E and GM 9.5" 14-bolt.
On a different note you have atleast 25% drivetrain loss. That puts the HP at 266 and TQ at 386. Far closer to the 290/410 rating than 240/340.
The fuel pump wiring being undersized and creating high resistance is a known issue and often the pumps have seen better days because of this (low fuel pressure is the result). The MAFs get dirty and under report airflow. Also the factory injectors tend to give issues. Factor in a distributor drive gear that likes to wear and possible tired ignition parts and that only means you can make drastic improvements without diving too deep into the engine.
Hypertech's dyno testing of a stock 2000 C3500 454 gave 215 hp @ 4,250 and 320 tq @ 2,000.