Stuck Fermentation on Big Brews

Relatively new to brewing & have had issue with stuck fermentation on most of my high gravity beers (1.090+). I have used Safale, Wyeast, & Whitelabs yeast, dble pitched, even mixed a dry & liquid yeast & they all seem to carp out at the 1.030 mark.
I know the yeast are fatigued from all of the sugar & elevated alcohol but I don't know why it always shuts down at that same mark...I have had little success with the champagne yeast breaking down further but this seems like my homebrew store's fail-safe plan...I am looking for alternatives
I also heard of holding back on the second yeast & pitching that after the first slows down...any truth to that?

Sometimes if you have beers with highly kilned malts, the un-fermentable or caramelized sugars in the malt will throw off your reading. Also are you using yeast that have a high tolerance to alcohol? Are you making a starter?

How long are you waiting before you take a gravity reading? Also, are you making a starter for your yeast and stepping it up to get the right amount of cells? Do you use Mrmalty.com? Just throwing a few things out there to see what your yeast pitching procedure is like.

Are you transferring to a secondary? If so how quickly? What's your timeline like?

A couple things you can try that might be of help.

Wait to transfer to a longer time. That much sugar needs a long time for the yeast to process.

Get a starter going with yeast nutrients to get the yeast active before pitching. Also make sure to aerate your wort prior to pitching.

Rouse the yeast after fermentation slows by gently swirling the carboy/bucket.

Increasing the temperature to around 70.

Thanks for the great responses... my mistake it was Safbrew yeast.....I have not made a starter b/c of time constraints... I add Wyeast Yeast Nutrient to my boil...my temp usually never drops below 70 in my brew/basement... I usually keep my beers in the primary bucket for 14 days then rack, maybe for 10-14 days if I'm dry hopping. My Winter Strong Ale I let sit in the p-bucket for 30 days then racked (I switched from a blow tube to an airlock after I took a reading two weeks in & it still didn't work it's way down from 1.030 on day 30!) Looks like my solution is to grow sum & make a starter, let sit in the primary at least 3 weeks, then rack...

I have never used Super-Kleer KC Finings but is worth it use or will the added time in the primary ultimately clear my beer... BTW is that Burton Ale a clone of DFH B-Baton, if so care to share?

Final gravity of around 1020 for big brews seems very normal. The brew I have bottled last week FG is 1019 where the OG was in the 1080's.

What I can think of, (and I am sure I am stating the obvious):
1. Yeast, does your yeast have the tolerance for the alcohol? Even Safbrew yeast has max alcohol tolerance. 2-3 11g packets should have been pitched without a starter into an oxygenated wort that is wormer then room temp with yeast neutralizer (that for OG around 1090).

2. Not all gravity is fermentable, if you did not use extract, then how did your mashing process go? Did you hit and keep the correct temperatures?

ehhh... give us more information... :+)

I have no idea if the following question is going to help you or make me look like one of those annoying know it alls

This question has 2 parts:
Part one: What is yeast Attenuation?
Part Two is: What is the Attenuation of your yeast?