Not to belabor this too much, but I wonder if the progressive nature of the throttle on the H-W might be causing this issue.
Consider this chart. At part throttle, the single barrel Rochester has a larger throttle area than the H-W, then as the secondary throttle plate opens at higher settings, the H-W has a larger area.
I expect this would cause the H-W to feel a little soft at cruise, but be equivalent at WOT.
I've not driven one - I sold the truck I put an H-W on before I go a chance.
regards,
Leon
