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

[USMC302]

What kind of rockers are you running and what did you do to check the pushrods? The first issue sounds like you might possibly have a collapsed lifter, I had a guy that over revved once and had the some problem you described and once he pulled all lifters, he found 3 collapsed. Also, what are you using to monitor A/F ratio and what does it read on avg throughout your RPM range under WOT? Are you using an electrical FP gauge or a mechanical?

[gtnby2]

Stock stamped steel rockers, took the push rods out and rolled them on a flat piece of glass and inspected the tips for straightness. I have a autometer A/F meter hooked to left and right banks through a toggle switch so I can monitor each side individually and the fuel pressure gauges are mechanical under the hood and electric inside on the a pillar next to the A/F gauge. A/F under WOT used to stay in the green gradually climbing until shifting, now it goes green, but stays steady not climbing so it makes me want to look at the fuel system as well as the lifters. A friend brought up to me about the fuel filter. I got a new one to put on...just havn't done it yet. BTW, on the autometer gauge, red is lean, yellow is styochromatic, and green is rich

Auto Meter Ultra-Lite Digital Gauges: ATM-4375 - summitracing.com

[USMC302]

You need to get a digital A/F ratio meter so we can see what it's actually reading, and change the plugs as well, just in case there are a couple fouled. Since you don't have an adjustable valvetrain, or bent pushrods, I'm sticking to my original diagnosis of a collapsed lifter. Lifters are fairly cheap but, not always fun to replace. Sounds like you have two different issues unfortunately.