It would appear that there are 3 of us with similar results...Our 454's are all losing power when loaded...Mine is a 96 with 150k miles, has the vortech tpi, 8 injectors to screw with. See post below, myself and this gentleman can't figure out anything usefull either.
http://www.automotiveforums.com/vbul...d.php?t=238530
I am really leaning towards the cat's (mine has 2 from GM) but really don't want to spend the bucks to replace if no good results. Dirty injectors are always a good possibility but how do you test? I have replaced the fuel filter, plugs, wires, cap/rotor, o2 sensors (all 4). It just doesn't get any better.....