A gooseneck is equivalent to a fifth wheel trailer as far as tow capacity is concerned.
To answer your question we would need more information on the truck, which I gather is a Silverado 1500. since the 2500 does not have that engine? What type of cab (regular, extended, crew), what bed length, rear axle gearing, etc. This truck is probably at or very near its max fifth wheel towing capacity with a 7000 lb trailer unless it has the 4.10 rear axle gearing.