Ignition or Fuel system problem ??

[Robert8096]

I have a 69 Stepside with a 283 3 speed with a 1450 Holley carb, the original point type ignition and 3.73 rear gears.

It idles fine, I can pop the clutch and smoke the tires or take of normally with no hesitation and go through the gears (either regular or hammering) and the engine responds well up to about 60mph or around 3000 RPMs, after that it will start sputtering and backfiring through the carb and in some cases die. I can pop the clutch and will start running again and will be fine until I reach the above speed again and then it starts all over. I can cruise with no problems until I pass 60 on the speedo.

I have owned this truck for about three months and when I got it the speedometer was broken and I guess I was driving it like a little old man because I did not notice this problem before I did the following:

I replaced the speedometer. ( don’t think this is the problem)

I added a tach. ( disconnected and it did not make a difference)

I upgraded the Holley from a manual choke to an electric. ( the positive lead for the choke is not connected to the coil) I blocked open the choke plate for testing purposes to make sure that the choke was not closing.

I pressured washed the engine ( covered the carb and distrubtor) done weeks ago.

I added a clear fuel filter ( temporary) to see if there was trash or rust coming from the tank and I don’t see any in the filter. It has fresh gas in the tank. Have not tested fuel pressure.

I did the carb spray looking for vacuum leaks and checked all the vacuum hoses for cracks. Nothing found.

I replaced the coil and did a visual inspection of the points and saw no issues ( I have since ordered the parts to switch to HEI)

I tested the voltage to the coil and it has around 5 volts with the key on and 9 volts with the engine running. I did notice that I do not have the wire running from the starter to the coil to supply 12 volts during cranking but it will crank on the second revolution when cold and one when it is warm.

According to the voltage gauge in the dash I see no extra or loss of voltage when this happens, it is always 11 volts or better.

With the above information what is your opinion, suggestions ?

Thanks
Robert