Fuel pressure problem..I'm at a loss.

Does it do it worse in any particular gear?
ie is it related to how much time you spend at WOT in a particular gear? and thus to how much heat is being generated.
Or is it strictly related to, after the engine has returned to idle/near idle, after that 1/8th mile of slowing down... assuming while still in gear?

The reason I ask is because I have seen this;

Slowing down for an extended period of time with the throttles closed, will cause a lean situation. If the Transfer-slots are also shut off, then very lean.
So the rear wheels are driving the engine lean, but the rpm is still high. So the fuel-pump is still working overtime, dead-headed.
While this is going on, the sparkplugs are getting hotter every second, because of the high-rpm, low gas situation. Finally, arriving at an rpm that you want to cruise at, you open the throttles; which starts up the low-rpm circuit and maybe the mains. When the cold gas hits the hot plugs, anything can happen.
Of course the pump is still deadheading.
IMO,
if the line from the pump to the carb is under pressure, it is impossible to vapor lock. But if the pump has been sucking the tiniest bit of air this whole time, with the float valves mostly closed on the closed-throttle shut-down, that air is now past the pump, and the pump has lost it's prime.
I had this happen to me years and years ago, on a mostly stock system.
And what I found was that the rubber jumper from the sender to the hard line was not sealing. Since it is at the highest point, it did not leak at shutdown. Since it was a tiny leak, the carb seemed to have enough fuel most of the time. And since I'm a streeter and never on the gas for more than say 5/6 seconds atta crack, I never noticed any of this. But the first time I ran 14 seconds at WOT, pow! I had trouble.
Now, I'm the guy who put that new jumper on there, with two correctly sized gear clamps. So I installed two more, total two per side,and rotated them so that the screw heads were 180* from eachother.
Badaboom no more trouble.
Don't know if it applies or helps but I thought it was worth mentioning.