hmm wish i could figure this out

 

it could be 2 things.

Fuel supply. there could be a lacking fuel supply as with no plate and a gutted AFC housing the demand for fuel may be more than the pump can supply

it could be dumping enough fuel to put out the flame and cause it not to ignite the fuel .

the second thing it could be is Timing. a truck at stock timing or slightly retarted, some trucks will retard over time as timing slips. get a shop or someone that has the tools to make sure you are in the 15-16* range.

 

a manual wont cause it to not build boost i can built almost 20psi standing still in neutral

 

what??? i cant... about 5 pounds if i really hammer it.

 

my auto in neutral at 3100 will build about 10psi....

 

Im guessing your running out of fuel. That or your timing has slipped a little get it re timed or bump it to 16* or 17* if that doesnt fix it try a fp Guage. I had a buddy with a miss around that RPM but his was from the 131dvs and 370 injectors.