I got this car in pieces and spent a year restoring it. It originally was a 6 cylinder with a 3 speed on the column. I put a 350HP 350 with a TH350 in it.
I removed the 5/16" sending unit and installed a new 3/8" and ran new 3/8" hard line all of the way to the Edelbrock mechanical fuel pump. I covered all of the fuel lines where they go next to the headers, so I don't think there is any possibility of vapor lock.

When the temp. is over about 70 deg. F, it revs fine in 1st gear, but seems to run out of fuel in 2nd gears and stops pulling which continues into 3rd gear. If it is cold out, this car runs fine through all 3 gears...pulling HARD all the way to 5500 RPM.

The engine is a .030 1971 350 with 882 heads 1.94 intake, 1.50 exhaust 76cc chamber. Flat-top TRW pistons. Comp cams XE268H cam. Edelbrock Performer RPM, 750 Edelbrock carb. Shortie headers with 2 1/2" exhaust. 34 deg. of total timing...MSD 6A ignition(Tried different timing)

I have had the carb apart several times and adjusted the floats, checked filters, just about everything I can think of. I haven't tried to re-jet yet because the spark plug reading looks good.

Anybody have any ideas?