Update on my dud of a rocket.

 
OMG! I was driven crazy and no dealer could find the issue with my 2010 roadster. Several thousands in failed diagnostics, changing the obvious fuel position sensor, throttle position sensor...changing each with no success. Turns out it was the clutch lockout switch!! Who would have thunk it??
 
The clutch switch is tied in with a whole load of things. I discovered that years back when the fuel level on my Roadster stopped working, and that also happened once on my 2.5, but I've never heard of it causing an issue with the venting of the tank. Is that what happened with yours @zenbiker ?

Otherwise, I'd suspect the gas cap, vent hose, or charcoal canister. You shouldn't have to do your own work while under warranty, but I find it usually saves time and is faster in the long run. It's not going to void your warranty, doing small things like that. Find your vent hose- is it kinked? Is it clogged?

A little hissing in hot weather seems normal, but otherwise something is restricted and if the shop hasn't found it and points to the ABS (WTF?) I'd suggest going at it yourself. My money is on what happened to @stingray - your vent hose in kinked and need to be slightly rerouted or replaced.