SR20DE cuts out at high rpm under load

[yeahyeah]

New here, looks like the SR20 forums are essentially dead, so I figured I'd try here for some hive mind troubleshooting. 

 

Running a sr20de (non turbo) from a JDM S14 Silvia in a Datsun 620 for endurance racing.  

 

Customer States: the engine acts like I lifted my foot fully off the throttle at about 5500 rpm, but only in 5th gear at the end of a long straight.  In all other gears it revs to 7000 willingly.  It doesn't seem like a spark cut, because it doesn't pop crackle like there is gas in the exhaust when it comes back on.  Seems like if I momentarily lift and reapply the accelerator it might pull past 5500, but there is only one spot on the track we run with a long enough straight to get there, and it's already almost to the breaking zone, so it's hard to tell.  5500 in 5th is already 120mph, so it's a little difficult to recreate the situation safely on the street.  Might need to buy some dyno time.  My first though is to look at fuel pressure, but it doesn't seem to stumble on and off, it just cuts off acceleration like a switch, so I'm curious if there is something in the ECU to look at.  Running a stock ecu.   

[fiveoneO]

Has this truck been running for awhile and this is a new symptom, or is this a new build? I don't know much about the SR20 so this is a total guess, could it be some kind of speed limiter? I'd try disconnecting the speedo sensor and see what happens.