[jlsanborn]

Man you've got a sweet truck and details like this would go un-noticed by most people. What you have now is an attempt at crankcase ventilation but is causing you a big vacuum leak at low-speed. You have three options....

1) Pull that line between your filler cap and carb and plug both ends. Vacuum leak is gone and you've got three crankcase vents (both valve covers and the filler cap). You won't blow gaskets but all three vents are going to be greazzy and you're not ventilating (fresh air) your crankcase.

2) Change to a non-vented cap and a filler neck with the hose barb and install the inline PCV. This will kill the low-speed vacuum leak and draw fresh air from the vents you installed in the valve covers.

3) This is what I'd do.... Fix or replace the script valve covers (no leaky holes like they oughtta be). Drill/tap/baffle the intake manifold (if you're sure your block dosen't have those provisions already) and install a PCV valve between there and one of the the big vacuum ports on your carb. Get the non-vented filler cap and the filler tube with the hose barb so you can run a line from there to the air filter housing. This will get you the best of all worlds! - no holes script valve covers, fresh air cross-ventilated crankcase, finely filtered ventilation air (your air filter as compared to the crappy screen/mesh in you valve cover vents or vented filler cap) no oil drippy vents or draft tubes = CLEAN. Who dosen't like clean?