If it helps at all, I am no expert but I did an RPO search a few months back to see if my 1999 Suburban 1500 LT had a towing package. From what I read on the internet, the RPO code for the towing package is Z82 (which I don't have unfortunately), but I do have code GT4 for a rear axle with 3.73 gear ratio. Based on this, it would appear you can get this ratio without the towing package. I also have this other equipment, which means it can be had without a tow package as well:
G80 - Axle positraction, limited slip
K68 - 105 A Generator (I think this is normal, HD is 130 A maybe?)
L31 - HD Trans cooling system
Perhaps some of the more knowledgeable posters can expound on this and confirm or correct my understanding as well. I also would be interested if anyone knew exactly what the towing package included...