As a general rule: the more HP you make on #2, the less HP you get from propane.

As an example. A stone stock truck can get as much as 100HP from a propane system. The same system installed on a truck with a big chip, injectors, etc. may see as little as a 30HP improvement.

You dyno'd at 380 (if I am remembering the right post), to me that means a highly modified engine with big injectors, turbo, maybe even some cam work. Without knowing your setup I'd say propane might not be the right thing for you if you're looking for a big power boost, NOS may be the answer you seek.

If better milage accompanied by a smaller power gain is your objective, then a low flow system triggered at low boost would be perfect.