Diesel Bombers - capped off resonator.....

I recently capped removed the plastic box ( the one that says 6.6 turbo) and capped it off and I am planning on doing the pcv reroute but last night while traveling on the highway my truck went into reduced power mode..... Is there something I should have done differently? I went ahead and stopped at a travel center and disconnected batteries and uncapped it and put the plastic box back on. After a total of 30 minutes with batteries disconnected I reconnected them and started truck and the engine light stayed on but had full power and no more issues. . . Any advice about this would be greatly appreciated