Hmm, maybe some of the more technical guys can help you out, as im still learning as well. My car has the "boat anchor" chevy 305 (5.0l) and she feels NOTHING like my daily driver which is a 115 hp, 2003 Mini Cooper. The zed 'feels' like a rocket up to 3000 rpm then drops off. I've dyno'd my car at 161 rwhp @ 5000 rpm, and 238 ft-lbs @ 3000 rpm, explaining why the car feels slower after 3000 rpm.
Anyways, my point is, with a 383, your car should be a tire-roasting monster!
Which shop did you take your car too? Sounds like they arent all that great. I'd reccomend ATEB in burnaby. I went there for some basic tuneup stuff, and they're friendly knowledgeable people. The shop owner Jon bought me lunch the first time i met him! It's somewhat of a small shop, but they do big business.