missing @ 3500 or higher when @ temp

[gtnby2]

I've had my 351 in for about 4 years now and recently developed a miss at higher rpm's. I noticed a slight "tick" in the upper engine about 3 months after switching to 5w-20 motorcraft synthetic that has gotten progressively worse but only after the car warms up. my first thought was the thinner oil was causing a lifter to collapse(hydraulic flat tappet) since when it was cold it didn't make noise. changed the oil back to conventional 10w-30 with a bottle of lucas additive and no difference; no noise when cold, noise when hot. I took the valve covers off and checked the push rods and rocker assemblies and all looks good. I hit 6800 rpm a couple of times so I wanted to make sure nothing was bent. I also noticed the afore mentioned miss or hessatation all around the same time so figured all the symptoms are related. Checked the timeing, TPS, Changed the wires and the spark plugs all look good but did not change them. A seperate issue I noticed today is from idle in neutral, if I goose it the fuel pressure DROPS until it returns to idle. Never noticed it before and I don't know if I'm noticing it now cause everthing is F'ed up or what!!I've had the same adj fuel pressure regulator(vacuum controlled) and 255lph fuel pump for years with no problems. adj pressure to 45psi without vac which translates to 40 with vac. A/F ratio looks good through out rpm range so I'm stumped. Bad fuel pump? Bad lifter? Bad spark plugs? Bad coil not producing enough spark? I need some ideas cause I can't just throw money at it....HELP!!!
thanks,
Brad\ GTNBY2