I struggled with the very same question last year.....decided that the Denali had just a few too many options I didn't want for an extra 10k. I ended up building my own SLT premium plus (package adds 7 speaker Bose with sub, running boards and 20" wheels).....the SLT comes with just about every other option and I added the 6.2L and 8 speed. Msrp was 54 and I think I only don't have sunroof, retractable running boards and MRC.
2016 6.2L 8 speed.....95% of the time I really like it, shifts smooth yet firm enough. Actually, I find it upshifts quite well, it's the downshifting that can sometimes be an issue. When you get on it, sometimes I feel it's sluggish to drop gears, but much more importantly it does have that hard clunk downshift every once in a while when coming to a stop.