[DaveB]

After about 75 miles I took off the Upswept Silencer and replaced it with the OEM Silencer on my 2013 C5 Classic Chrome. The Upswept added a little more exhaust note but I noticed decreased performance above 40mph. I noticed more vibration at speeds above 55mph and the best I could get out of the C5 was around 72mph with the Upswept. I think the UCE likes a little more back pressure than the Upswept Silencer offers or maybe I need less intake restriction to take full advantage of the less restrictive Upswept Silencer. The C5 now has almost 1300 miles and is sure running sweet. I just changed the oil and I'm using Agip 15w-50 semi synthetic.

[High On Octane]

75 miles might not be quite enough time for the computer to relearn the new muffler.  Maybe.

[Norm]

+1  That was my experience as well.  I was told that the computer should figure out the upswept muffler fairly quickly, but after a couple of hundred miles it was clear that it was not the case.

In retrospect I wish I had spent more time getting fasteners and wiring more secure and less time with airbox mods and filters.