FUEL...AIR...SPARK!
I'm assuming Cory put alcohol tolerant injectors in it when he did the 368 upgrade, so (for now) I'd want to verify dynamic fuel pressure FUEL PRESSURE first: Harbor Freight can supply a fuel pressure gauge and an extension hose so that you can tap into the fuel rail test port (front end of the passenger side rail). Then you can tape the gauge to the windshield and go for a drive.
Cruising at around 50-60 ish mph the pressure will be ~ mid 40s (mine hovered around 45-46 psi @ 45-50 mph).
Slapping the throttle wide open and the pressure leaps to the 53-55+ psi range.
If you pressure(s) are low, especially on the WOT portion of the test, starvation is the issue, and you want to address that ASAP to avoid serious issues resulting from a lean situation...ask me how I know!
I wanna say, one of the best damn tools I ever bought for my Z was a scanner capable of OBD-I reading!! Having one will really cut to the chase! I'll have to defer to others Marc Haibeck, or Dominic or Pete or -=Jeff=- for a recommendation for a suggestion (as my AutoXRay unit is no longer available).
OK, fuel pressure OK, and no scanner, spark plug condition comes to mind. By reading the plugs, they can often give clues as to one or ALL cylinders operating condition.
Again, here's where a scanner pays for itself, look at the O2s: checking for uniformity in operation, and cross counts especially, and they should be in the hundreds. (An O2 with low cross counts indicates a lazy O3 sensor. For verification, you can swap them side to side and re-test. If the one lazy O2 is still reading low cross counts, then you have located at least ONE potential issue.
A NOID LIGHT will let you know if you have a cylinder with a weak spark, along with the plug being wet or sooty - confirming what a noid light is suggesting.
Coils: (see attached) Waste spark = two plugs firing simultaneously as each coil is attached to two plugs in series:
1&6, 4&7, 2&3, 5&6.
Resistance (AC/Delco) between spark plug (secondary) terminals ~ 5.2kΩ, but resistance between (primary slots) only ~ 1.5Ω. Resistance between primary and secondary is infinity (or better be!).
Note: A common issue is for the secondary side to be open. If that happens, the spark may jump the break internally, but the resistance (air gap) will impede the current to the plugs resulting in a weak spark. Replace one, replace them ALL! ( If one fails, chances are they are at the end of their life expectancy and it is safer to change them all - take a chance on the new electronics "infant mortality" - and not have to troubleshoot each of them again as they fail. Just a thought. (Folks have had good luck with MSD products - or they used to before they were made in China).
It all this checks out and the issue remains, we can take further steps...