SR has an intermittent miss at 3800 rpms..ideas?

[Dustbunnie]

I've had my swap running since about April, and over about the last month or month and a half, I've been having an intermittent miss that only seems to occur in the 3800-4000 rpms range when I'm getting on it, with varying severity. I had a bad coolant temp sensor which was causing the car to run funny on cold starts and which I thought was related to the miss problem. I tried pretty much everything..seeing if the spark was ok (seemed to be rock solid), ran sea foam through the top end and the gas, new bosch platinums, it has a 3-month-old MAF I bought from where I work (SOHC KA one)...but anyway, I'd do these other fixes and I would think that I solved the problem, yet it would come back late at night when it got cold out..hence me thinking it was the temp sensor

So I replaced that and all seemed to be OK, but I noticed that it still has the miss only when I run the car for the first time on a given day, for maybe the first trip (first 15 mins? I'm not real sure)...the only other thing I could think of could be the oxygen sensor...since it seems to be the only other tune-up type part I can even throw at the car anymore, and since maybe the problem is occuring when the sensor isn't in its heat operating range or whatever that is...

FYI, I have a redtop S13, front mount IC, 3" turbo-back exhaust, walbro pump, running 13 psi on a manual boost controller...greddy type-S which is recirculated..if that is pertinent at all