rt 14 east of cedar city

I think that is the road where I saw (on youtube) a 5th wheel stuck on a hairpin turn.

You will find 14 to be steep and very narrow, little if any shoulder for much of it. If you have any sort of problem there will likely be no place to pull off. There are other roads that are better suited to the OP's rig. Can you pull a large rig on this road? Yes, but just because you can does not mean it is a good idea. :R

On Google maps streetview I see a sign at the Cedar Breaks junction warning of '8% grades' and '25 mph curves' ahead on UT14 (west bound). My impression from online samples is that Mountain Directory relies mainly on signs like this.

8% for shorter segments is consistent with a long distance average of 6%.

I only see one pair of S curves that are tight enough for 25 mph. That is just above the Cedar Canyon campground.

143 heading downhill toward Parowan has a much tighter pair with 15mph signs (and 'not recommended for trailers' and '13% grade' signs in the ski village). 143 the other direction (toward Panguitch) is a pretty drive. Much of it is high altitude prairie, passing by relatively recent lava flows. I don't recall any significant curves or grades - but I was in a car that wasn't bothered by such.

20 is an excellent way to get to I-15.

I don't have my "Mountain Directory for Truckers" handy but I would guess Hwy 14 is more than a 6% grade.

We drove it last fall without the trailer from 89 to the Breaks, then down to Cedar City and back across to 89. It has some steep grades and is a bit curvy as well. I wouldn't want to pull the trailer on that route, and I have pulled all of rt 12. The Breaks are neat, but are very 'Bryce' looking. Steepest section is from 148 westward if I remember right. The section from 89 to 148 was not as bad, but will still rise about 3500 feet.

According to Google Maps and http://www.gpsvisualizer.com/profile Cedar City to the Cedar Breaks turn off is 28km, with 1200m climb, which averages 4.4% grade, and closer to 6% in upper half.

If going west U'll be going down the mountain. Kinda steep, just take it slow. Shouldn't be a problem. If going east be sure to take Rt.20.

We always use hwy 20. Less curves and steep grades than 14. However, still requires low gear.

The turn off to Cedar Breaks is the high point on 14, with the park itself being a bit higher. Further north on US143 you can turn off onto a gravel road to the top of Brian Head, one of the highest spots in Utah that you can drive to. Beyond that the highway passes the Brian Head ski resort.

So the ski resort and the park are best sources of information on snow conditions in this area. The road through the park is not plowed in winter, but 14 itself is plowed, as is 143 to the ski resort.

20 is the easier way across this range. But if you are comfortable with mountain driving, you'll handle 14 just fine. And if you want to seek the Breaks, then 14 or 143 are your only options.