I own a 2017 Colorado diesel and I've asked GM about any issues due to accidental overfilling the tank and having fuel way up into the fill tube and I cant get an answer. I'm curious as to any issue causing problems like you'd have with the evap system on a gas engine. I have an extended warranty good to 100,000 miles so I dont want to do anything that would cancel the warranty by doing something like adding an extra fuel tank in the bed which would feed the tank with an aftermarket "Y" fuel fill tube. Fuel is a lot cheaper in Ky and I'd like to add the extra tank to take advantage of the cheaper fuel. Any thoughts?