2010 Sierra 2500hd rclb. Has plenty of power and bigger than factory brakes. Looking to upgrade to a 272 formula or 311 formula. I think I'd be just fine with the 272 but if I found the right 311 am I still alright?

Shouldn't be an issue.

They don't build a boat big enough to stop a Duramax

Last year Gordon and I towed his 38 Top Gun twin step with a 2011 2500HD Duramax. We took it from NH to CT last year and it tows that boat perfectly well. The quality of trailer makes a big difference as well, his boat is on a steel Myco.

2010 RCLB, is rated for 13,000lbs bumper pull and 17,500 lbs fifth wheel. Your fine with both of those boats. Word of caution the factory hitch is only rated for I think if I remember correctly 7500lbs bumper pull.

I have a Curt Class V on it currently

I just honestly wasn't sure with the cab configuration if it'd be enough truck or not. I know ice pulled bigger and heavier than either of those two boats, but not for long periods of time

despite the GM handicap you will be fine! I towed my 32 fountain (with trailer around 10k#) behind my old 2001 f250sd 4dr 8 ft 7.3 for several years with no motor mods to it 70pmh down expressway without problems. Still no problems with motor, trans or rear but did add some mods last year to update and for fun!

Are all your expressways downhill?

No problem for a 311. I tow my my 32 AT with a 2007 2500HD 8100/allison. Its 8k dry and 11-12k on the trailer.