History: Have a 70 Chevelle with the 5.3 LM7 Iron block. Got the above system and installed with a single-plane from Holley. Sat for a couple years due to life getting in the way. Recently, I was able to get back on the project. Drove it around the block to shake it out. Occasionally, while starting and let it warm up, shutting it down, restarting, it would "pop" back through the TB. Scares the wife and dog. But it would start on the next try. Until today. I took her out on her longest run yet, about 10 miles, nothing fancy. About 7 miles in, I was at a light, and begin to accelerate when it backfired, loud and it died. for the remainder of the trip it would stop running at lights and when I tried accelarting. At one point, thankfully, near my garage, at cruise, it backfired and quit. Back in the garage, I looked into the throttle-body and found the expected soot in the TB. It never overheated, no leaks, fuel pump was at the correct pressure (43). If it was a Gen 350, I would have checked the wire order, but it's not, and I did verify the coil wiring. My other though is valves not closing. I didn't have time yet to check the plugs, previously discussed wife was waiting on me. I will fire it up tomorrow and after it's warmed up, check the plugs. Anybody got other suggestions or had similar experience?