Fuel flow problems

[rwenner]

I'm having problems with my 1967 T337B fuel flow at alt's above 9500
conditions: 30 min into flight after cruse pwr and leaning (26" 2300rpm and 10.3 gph) fuel pressure and flow drop and the engine tries to stall out. This does not seem to happen at lower alt's and can be fixed by turning on the low boost aux pump.
Items checked or OH to date:
Engine driven fuel pump OH and retested.
Upper deck pressurers checked and adjusted
Fuel distributor inspected
Vent lines and check valves tested clear
Fuel strainer cleaned and OH
Fuel filters replaced
Injectors cleaned and O-rings replaced
New plugs and ignition harness.

Where next guys?