I'm not a huge fan of Champion rads, I have never used them but i have had customers that have. I think they are to restrictive for Alum rad, but i would say they seem to be the best of the china rads. Personally i would have gone with there American eagle version with the 1" tubes. This would help increase the flow of water. Next i would have a 1 3/4" lower hose fitting installed.
I'm sure Summit will take the rad back, they are good about that.
Just so you know i had a customer pull a rag out of a brand new rad. You really need to get a IR gun and get some measurements.
Good luck on the trip, i hope it runs cools. It will help to change my mind on Champion rads.
I think the comment about the exhaust is a good one. Have you noitced a decrease in power lately? could be a pluged up cat too. I had a new high flow exhaust done on a BBC dually years ago, along with a huge power increase it did seem to run cool when climbing hills.