gnappi

There's a Trek Fuel EX 5.5 locally and while I don't ride trails, my hard tail mtn bike is tough on my tail in the suburban routes I take. The price seems attractive @~$400 but I'm conflicted on whether or not it would be an upgrade over my F300 Cannondale for my tailbone :-)

Does anyone here have or have had in the past a 5.5 they can comment on?

2cam16

I've never owned a 5.5 but I have an 8 from 2011. They seem to have some similarities (120mm travel, some of the frame design,etc)
Just make sure the shock and fork are in good working order. No leaks, etc.etc. Also not sure about the 5.5 but my 8 had a proprietary Fox shock in the rear. Trek and Fox had the shock specifically designed for the bike and it's hard to find a replacement for it. Overall though I loved the bike until my shock gave up and finding a replacement unit for it is beyond my $$$. Riding for me was firetrails and singletracks, jumps,etc.etc. I'd do some research into the 5.5.
Hope that helps a bit.

Darth Lefty 

That bike spans a lot of years and has changed a lot in that time so it's hard to have a solid opinion without knowing more. But generally I think a trail bike wouldn't make a good commuter. It would be a soft ride but it's going to be heavy. It won't have any provisions at all for accessories like racks or bags or fenders, but you could clamp a rack to the seat post.

There's a history of trail or XC bikes used on the street. Cannondale did it years ago with a full suspension version of their Bad Boy. MTB-style e-bikes are common now too.

Edit: 'pon reading some more it seems this is a 2008-9 base model with a mid-2000's frame design. Components are good enough to last. It has a coil fork, so as long as the shock holds air and nothing rattles it should be good to go. MSRP was <$1400 but the old-when-new frame and the rapid change of MTB's this decade has made it look dated.

Darth Lefty 

It also just occurred to me that your hard tail is probably a 26" wheel bike, and you might be running tire pressure pretty high for the street. Try bigger tires and lower pressure - Schwalbe makes some really big cruiser slicks (Big Apple Plus) you can run at 30 psi. If you still want to switch bikes try a more current hard tail with pretty big wheels - like 29" big, 2.3" wide - give it a shot. It smooths things out a lot.