First off, get some exhaust on there. Those fumes can kill you. Having said that. there's nothing like the sound of open headers. I don't like them on break in since you can't hear something before it becomes too late.
In any case, it does sound as though it is jetted too big. I'm assuming you've set the mixture screws to highest idle speed or highest vacuum reading, either will work.
Is the truck driveable? I would suggest jetting down 4-5 sizes and going for a 20 mile drive. Should clear the plugs and give you an indication of how total air/fuel ratios are doing. If it starts stuttering and stumbling immediatly, go home since it's probably too lean.
Holley makes a nice assortment of jets from 60 or so to 99, ive used it quite a bit over the years to tune cars in.
Devin
