Cetane rating specific gravity. 44

[rbdjr]

Has anyone measured the cetane number on the fuel they been getting, GM recamends cetane number of 44, I cant seem to find anything over 40, then I played with the sample fuels I have and added Archoil, Amsoil, Hotshot, and added 1oz of the Archoil, 1oz of the hot shot 3 oz of the amsoil to 2 quarts of diesel fuel to see if any of them raised the cetane number with my OTC diesel fuel Hydormomiter. Did any of the factors affect the measured specific gravity number to increase the cetane number? Is this normal, as they all say they raise the number 4/8 numbers, no change on all? I'm not a chemist but was hoping to see maybe 1 cetane point higher, not sure how additives raise cetane ratings, note I have NO Top Tier diesel stations within 3oo miles of where I live in NJ. 20 years ago when working at a gm dealer we would not diagnose any diesel if we did not have a rating of 43 or higher? Has fuel quality dropped? Been teaching auto at a VoTech High School, and we are testing different samples of fuel seems 40 is the highest? It is mid-April here in NJ. I'm thinking the winterized fuel is gone, as all 4 samples I have taken from busy stations.
Anyone else check the cetane rating lately?

 

[HacksawMark]

I don't have a diesel fuel Hydormomiter so I haven't checked mine. I use Opti-Lube XL and XPD to raise cetane and lubricity when on road trips. At home (western Oregon) I always fill up with renewable diesel which is supposed to have higher cetane than diesel #2. I've been using XL for lubricity. Seems to run smoother than just diesel #2. So the question is: are these additives just placebos or do they work?