A quick history....
Car is 85 Corvette, L98 TPI

Did head, intake, rocker arm, & longtube header swap.
Car should easily make 275rwhp/375rwtq, probably more.
(It made 239rwhp/359rwtq w/dyno issues highlighted below)
Car originally had some vacuum issues, since taken care of.
Car wouldn't go into closed loop.
Traced it to bad injector connection in header tube that had O2 bung welded into it. Fixed it.
Car ran excellent.

Took car to dyno and only change was filling up gas tank for the drive.
Find 40hp in my buddy's blower tune, can't wait to caveman tune mine (FP and timing).
6 passes on dyno, all of them at mid to high 12:1;s, but then with severe misfire/very erratic AF readings at 3300 rpm's, then by 4000, over 14:1 AF and no power. Car does NOT lose fuel pressure when it goes/shows lean.
I had some brand new injectors anyway (24's), so I swapped them out. No difference.

Even though most items were changed during head swap, I swapped (again) the plug wires, plugs, cap, rotor, coil, fuel filter. I even re-adjusted valvetrain. Originally at 1/8 turn past zero, now 1/2 turn past zero. (Hydraulic flat tappet stock cam w/1.6's)
Car still misfired and wound up melting catalytic converter guts.
Opened exhaust up, car screamed...for a day or two...again.
Misfire returns...

Swapped TPS for known good one, no change.
Tried advancing and retarding base timing, no change.
Upped and downed base fuel pressure, no change.

When it misfires, it backfires and/or pops through intake and exhaust at the same time. I can best describe it as the sound of a blower car getting spark blown out, or a wiped cam. If I ease into throttle, up to 5800 rpm's, it doesn't misfire. If I rapidly open throttle, it misfires at least half the time, maybe more since it seems to be getting worse.

Charging system is fine. (14.2 volts at idle)
Fuel pressure doesn't fluctuate at all at WOT (38psi)
Timing at stock 6*
Misfires only at WOT (or at least that's when I can feel/hear it.

Any help greatly appreciated

That happened to me and it was the EGR.

whatever is happening, it's going real rich as the RPM rise. I wonder what the O2 is seeing/doing.

Actually, the wideband readings show lean as the rpm's rise, and as the misfire happens:

I tried to datalog today using the WinALDL program. Laptop kept shutting itself off for some unknown reason...

Here's what it sounds like...does it now even sitting still just revving it up:

http://www.youtube.com/watch?v=hD4R08CVQDw

hm... the O2s are seeing lean, yet the car is going rich.

that's odd.

Problem was finally found and verified yesterday....

Wiped cam lobe.
Now I get to pull it 3/4 back apart 3 weeks after getting it together....

wow. that would do it.

I hope warantee is covering that junk cam. that sucks.