I have a 68 notchback 318/340 heads,cam,header's etc.It run,s really strong for what it is. for 2 or 3 year,s no problems but lately i may go 5 miles or 500 and it loses power like its running out of gas. will idle ok but when you give it gas just wont take it. sometimes after sitting hour or so will start right up and run right all day or 5 or 10 miles.put new fuel pump on it already after problems started trying to sell it but need to fix problem first, any ideas?