engine falls off at 3600 rpm-need help!

[into69z]

This may be a long story but I will try and shorten it. I rebuilt a 74-454 motor for my 69 c-20. Great machine work, all new parts and it doesn't perform as it should. At 3600 rpm, the engine acts like you run out of gas-like when you run the bowl dry and the pump isn't keeping up. The truck has 7000 miles on it since rebuild. Seems to run fine until you get on it then it nose dives. I took it to a dyno shop and had everything checked out after 500 miles of running/break-in. I will post the results and what they said might be a problem. They did the first run just as I drove it in-then found it dropping off, they ran a fuel line from the pump to a 5 gallon gas can to eliminate the trucks tank etc. it helped as you can read in the tests but didn't cure the problem. They checked the valve train and valves were adjucted fine and the valves had good seat pressure(comp cams-everything was new) they found the guide plates on two valves broken so new GM units installed. They said maybe it's a cam timing issue. I know the cam was set in according to comp cams instructions. One thought I had is I bought one of those 65volt "china"made HEi units-I wonder if that distributor is crapping out? I know it's been like three years ago since I did this rebuild and swap from a 350 to a 454, but it only has 7,000 miles and it's not getting better. I now have the time to focus on it so that's why I want to fix it. The motor was built to 74 specs with 781 heads, comp cam xe262H-10 kit, edelbrock intake and 750 carb, headers etc. This motor runs fine till you get on it with no additional issues. I am open to any ideas to checkout( I did call comp cams when I was building everything to ask if I needed to degree the cam , and their tech said I would not gain anything, that put it in straight up and your good to go) Take a minute and look at the dyno runs-it's got me puzzled.....Steve