HELP!! '72 Chevy C-10 engine ‘cuts out’

[Miles]

Greetings!

I have a ’72 C-10 (3 speed on the column) with a problem that has been tough to diagnose.

Problem: while driving on the highway at a steady 60 MPH, the engine ‘cuts out.’ This lasts for anywhere from 2 to10 seconds after which it starts to run again (it jump starts since I usually have not taken it out of gear). It seems to occur after I come over a rise in the road and am backing off the throttle to lower the RPMs / remain at the same speed (it does not seem to happen when going up hill/ accelerating).

I suspect either an electrical or a fuel-delivery problem.

In trying to solve the problem I initially replaced the gas filter (the old one looked OK) and tuned it up; no help. I then had the Edelbrock carburetor rebuilt (it is 5 years old), and switched the ignition from the original points to electronic ignition, put on a new vacuum advance, plugs, wires, and again tuned it up – no help. The carburetor gas mixture seems to be correct. I have started to use a bottle of Lucas Oil gas treatment with each fill up just for luck!

The engine was replaced with a ‘crate engine’ 2 years/10,00 miles ago and ran well until about 6 months ago when the intermittent cutting out started. The cutting out can occur once or multiple times over a 20 – 50 mile stretch and then not occur for sometimes hundreds of miles.

I learned the hard way to immediately take my foot off the gas when it cuts out: if I don’t, once it kicks back in (jump starts) in it will backfire: I have blown out 2 mufflers, so far!

The reason I now suspect an electrical short is this: Saturday when I had come over a rise, it cut out. I put it in neutral rather than leaving it in 3rd. I noticed the radio had lost power and after about 5 to 7 seconds the oil pressure ‘idiot’ light on the dash illuminated at the same time the radio went back on. I then turned the ignition key to start it in neutral before putting it back in gear to avoid ‘jumping’ it. The battery is a 3 years old but is still good (lights work well when engine off/ the engine turns over briskly). How about something to do with the alternator since it seems to be RPM related (or is that coincidental)?

With respect to fuel delivery theories, could debris in the gas tank temporarily getting sucked up, blocking flow, and then falling back into the tank after the suction ceases? (The gas tank has never neen cleaned/messed with). More doubtful is the idea that the hose portions of the gas line are contracting (like some sort of vapor lock) since the problem seems to occur when the load is the lightest. Any thoughts about the about the fuel pump?

Thanks for any constructive thought/suggestions!

Miles