The early 90's 454 motors were very underpowered at best. I don't have the numbers here in front of me, but some were rated as low as 200 hp! Now, for your part throttle question...is it the stock catalytic converter? If so, take it to a muffler shop and have them flow test the exhaust. You could have a restriction or clogged cat. Check your air filter too, make sure it is clean. Also, if you follow your air intake pipe off your air cleaner, you will see a large "can" just before it exits into the side fender well. Take this piece off and look inside. There is an insert in there shaped like an hourglass. Remove that.