5/16 to 3/8 fuel line

i have my 360 (went from slant six to 360) in and broke in, theres a problem. It acts like theres not enough fuel past 4k rpm. i am assuming this is because i am still using 5/16 (slant six) fuel line? If thats the case what is all needed to switch over to 3/8. I already have 3/8 going from the feul pump to the carb. where or what company sells f3/8 feul line to go from the pump to the gas tank? also do i just have to put in a different sending unit into the tank? give me the lowdown