Need help!runs out of fuel at hiwy speeds.

[PAPA KENT]

Need some input guys,My 76 with stock 400 and carb. runs great going any where from 20-40 miles into town in the mornings when it's cool and on the way back home in the middle of the day when it's warmer while traveling around 65 it starts cutting in and out and when i slow down to around 45 it gets fuel again and i can make my way back up to 65 for 3 - 10 then back again.Today it was worse where it died several times and then i had to prime the carb again to get it to run at all. I have replaced the fuel pump 100 miles ago,replaced rubber lines from pump to carb and hav'nt replaced from sending unit to rear steel fuel line yet.Backing up a little on the history about a month ago i was pulling from the drivers tank and the return line was filling the pass. tank and over filling it so i by passed crossover switch and stayed pulling from the drivers side but it ended up where i had volume but not enough pressure to run so i "assume" the cross over switch was also pulling from the pass. side so i ran my fuel line from the pass. side which was a dead tank for who knows how long and this problem started.I have 2 inline filters and the mini in the carb so i don't think dirt is the problem.a good friend of mine said that his father has had this problem and it was the sock breaking down and cutting off fuel,or i think maybe the old hard fuel line from the sending unit.Lack of time has been a major factor here from pulling the tanks to replace the lines. and where can a guy purchase a new sock?

Any ideas would be appreciated.

Kent.