[KENSTV123]

Valid for "conventional" cars, but I don't think it applies to the Cruze. The Cruze has no flashers. That's all done by the BCM. The controls tell the BCM what you want to do.

OP, does the hyperflash happen for both left and right or just one direction? If just one direction, recheck the turn signal with as many lights on as you can. See if it works normally and has normal brightness. I'm thinking you might have a bad ground (perhaps caused by modifying the wiring for the trailer), or you have a old bulb that isn't drawing as much current as it should and confusing the BCM.

The last idea is that the trailer has somehow damaged the BCM ($$). But before that, I'd try disconnecting the battery for a few minutes to try and reset it.

I hate to say but the BCM was likely overloaded and damaged, the lights are all monitored for current draw, this involves a small value resistor inside the BCM port that drives the lamp, the resistor is in series with the lamp and the overload probably burned this load sense resistor which may be causing a false reading of lamp load which the BCM is using to set the flash rate, only hope is the disconnect reset IMO, also do not short the battery terminals together, this might damage the on-star backup battery