Stock jdm b20, b16 trans, t3/t4 57 on 7psi. Dsm 450cc. 255lph. I'm obd0 and turbo edit tuned.

I'm having an issue where my ef cuts out in 5th gear at full boost. I can get up to speed and put it in fifth and floor it up to 100 mph with no issues, haven't tested faster. The problem seems to only occur if I flog it through 3rd or 4th, then shift to fifth and get back on it. AEM wideband shows dashes when it happens (full lean?) and it falls on its face. No popping or breaking up, runs excellent. On one occurrence I got a code 3 (map sensor failure) but on the test right after that I had no code when it happened. Plugs gapped to .028, verified boost is never creeping past 7psi.

Please tell me someone has an idea.