Dave,
I had been following this until I thought you had it all fixed. Steve dropped me a note to take another look. I think Tony has given you all the right steps, and you have appeared to do the right things.
My suggestion was going to tell you to remove the sock at the tank, which you obviously have already done.
My first suggestion is to get rid of that small see-thru filter. They really were never made for a double pumper system. That alone could result in your fuel pressure dropping off.
Then I would strongly suggest going back into the bank account, with the Mrs.' permission of course
. Buy a simple electric Carter fuel pump - (Jegs's $69.99 # 180-P4600HP) Of course you can buy Holley, etc. but I'm giving you what works for the cheapest investment. Make a fuel pump block off plate for your Mechanical pump or just leave it in place.
Use at least a Holley style filter # 720-9745 ($8.99) Also available from Jegs. And if you really want to know what's going on you can put a small in line fuel pressure guage right at the carb.
Now my question is...when you pulled the pickup tube out of the tank and there was no "sock" on the end of it..what happened to it? Is it floating around in the tank? Or was it removed earlier?
You do have a CR's kit, right? If so that pick up tube came with a nylon sock on it.
Did you hear the story about Double Venom II at the DVSF? Damn, it wouldn't run over 30 mph at our Saturday events. We finally tracked it down that ATL, who built our fuel cell failed to remove the sock from the pick up tube! Pulling 58 PSI at idle, the pumped pulled the sock right up into the pick up tube!
If I think of anything else I'll let you know. A good test to see if the fuel is the problem, take her out somewhere where you can get into it a couple of times. If it drives just fine in city type conditions, then stand on it, and it then starts to fall on it's face, or starts to backfire and cough, it will most likely be a fuel starvation problem.
Good luck and Happy New Year!
DV