I'm looking to improve my uphill towing speed (hiway) and am wodering what combo would be "best". headers? single 3", dual 2 1/4", flowmasters, etc? Subs an '80 w/no cats, stock carb tweaked, curved hei, 4x w/4.10s, dual 2 1/4"s w/no crossover and old "turbo" mufflers. Thanks for all responses.