I'd think your CEL is on because the secondary O2 sensor is picking up the lack of a cat, but that won't engage limp mode. Maybe you're having an unrelated problem with your primary O2 sensor caused by bumping it or damaging it on the pipe installation. Could even be hot exhaust gas is leaking and burned the wiring. Check your MAFs in your CAIs to see they're not dirty or damaged or anything.
How's your oil level? You sure it isn't running low or that there isn't a leak somewhere that caused oil levels to drop?
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