318 Magnum Tuning help

Tonight is the first time I have gotten to drive my truck. I noticed it has a very bad dead spot where it just flat falls on its face no power horrible sounding. Below that spot sounds good runs fine above it inst terrible but doesn't pull like I think it should.

Here is what I have its a 93 318 with a .512/.522 lift 206/212 @.050 cam. It has a Holley 80457on it.

Timing is set at 10 degrees BTDC.

Its worst spot is under light load about 1/4 throttle, if you let out it does fine or step on into it gets a little better.

Where should I start for trying to tune this thing?