What did I do wrong?

Bought some boneless simmering rib strips from Costco today and thought they'd be great to slow cook...fired up my Memphis Select pellet grill at 225 and had them on for about 3 hrs. with a foil pan under the grill with some water in it. Added some sauce for the last 45 min. and cranked it up to 300 until internal temp was 145 (like it said on the package lable)...They tasted great, but were still kind of chewy and almost on the verge of being too dry...
My wife may make me get rid of my pellet smoker and just use a slow cooker!...I've got to prove her wrong in pursuing this line of thinking!

I would say they were not cooked enough

Boneless simmering rib strips, hmm.... sure wish the meat industry would get a handle on its nomenclature. Could these be boneless country style ribs? heck even that term may not be accurate ??? Could you tell what basic meat section these were cut from? Too dry after 3 hours suggests they were reasonably thin and possibly lower in fat content. If that's the case sounds like a direct grilling (in less time) might have been a better choice for them. Take care of the wife 1st! Smoke a pork butt, hard to mess up as they are very forgiving.

yeah I really dont know what meat you were cooking...give us a better hint and we can fix it

They were labeled as simmering short ribs boneless...marbled fat in them. looked just like large rib cuts would but I even expected there to be some bones in there!?? They were strips about ¾" thick and about 8" long X 1 ½ in wide
I had some today for lunch and noticed that I can still see some marbelling in the meat. Would this indicate that they should have been cooked longer? They still taste awesome!...just not falling apart tender like I'd hoped for. It might have been the particular piece my wife had last night too? Odds are that she'd be getting the gristly piece if there's one to be found <G>

beef? If you still saw fat then probably not rendered....one thing to keep in mind and I dont mean this as sexist but history around here has shown that most men prefer a deep smoky flavor......Im not saying that women dont like smoke but your wife is one of many that has raised the issue of smoke SO the three hour smoke is probably the wrong thing

What I would try next time is to cook the meat until you hit your 145 and then foil with a little liquid of your choice can even be a little beer. cook for an hour in foil and then sauce if you want and serve

The other possibility is that if they are telling you 145 is the ideal temp then that should be cooked fairly hot and fast...aka grill

Thanks I'll try the foiling thing next time...so I'm thinking then that as you say, the meat hasn't completely rendered the fat marbling. I had the rest of it the next day and it wasn't all that tough...so I'm thinking she just might have got a particularily bad piece. She did like the flavour though and likes smokey meat so I'm ok there.

Sounds like they were pork rib tips (which are boneless) from the racks they trimmed down to St Louis ribs. If that's the case then you didn't cook them long enough.