[Excaliber]

5800 rpm is pretty high for a "stock" 351W, 4800 was more like it. SO, if indeed it IS "still pulling" up to 5800 the cam is not anywhere near stock. Might be "timed" incorrectly to the crank as mentioned. The stock 351W 4V heads weren't "that bad" I wouldn't think the GT-40 heads would make a huge difference.

I would do the "basics" as recommended befor going in to deep. Throttle plates, cam/ignition timing, compression check (wondering what the C.R. is by the way?).

15 sec do sound TO slow all right. Gotta be something wrong (assuming it's NOT a stock 351W). Remember, it's not about a single component, it's about how ALL the parts come together. Cam matches carb matches intake matches exhaust, all that.

Ernie