Rb25det going into limp mode

[SethG12]

Ok I swapped my r34 rb25det neo into my s13 about 3 months ago. Wiring specialties harness everything was legit on the motor, put it in drive it for a good month to 2 months and it ran very very good. I don't get on it very much since it's my daily driver and it's a really clean shell that I don't want to smash up. We'll anyways lately my car started acting funny is start it up and it would sound like it's cammed for about a min then knew it warms up a little bit it'll be fine. But then once I get on the highway after about 20 min once it fully warms up to it's top operating temp it'll start to decelerate all the way down to 3200 (what my un calibrated tac says) then it won't let me rev any higher than that 3200 mark and if I do it'll sound like a "2 step" the car has a walbro 255 with stock fuel pressure regulators and wiring specialties harness and fmic. Everything else is stock. I've tried cleaning the maf with maf cleaner, unplugged the o2 and drove it and it still did it, unplugged the maf and it putts it into limp mode at a little higher rpm. My s13 doesn't have a data link cable to church check engine light, And my ecu doesn't have the indicator light or dial on it.