a couple of things come to mind
- you did use factory plugs not aftermarket ones right?
- have you checked the plug wires, make sure they aren't breaking down when they get hot. (usually they would start arcing against the engine head or anywhere they are close to the engine).

As for the fuel pressure? that sounds close to what it supposed to be, maybe slightly low. what is it doing when you accelerate? does it drop lower? or is it consistant?
if it drops then this could be the problem...
vaporizer/converter

good luck