My wife and I just took a 1500 miles trip towing our 2619 with our '97 4.3L auto/OD blazer w/3.42 rear. It did okay, but we did a lot of Tenn/N Ca mountains and it strained a bit. If you upgrade gears, you should be pretty happy. I changed out my 3.42's in my Astro and moved up to 4.10's and love it, even got better gas mileage ( but then I do have 31" tires it too). We ran at 65mph @ 2800 rpms with our current setup in the blazer, OD is a nono obviously unless you want a new tranny. You may check with a dealer or go to
www.fullsizechevy.com and check about the speedo correction after changing gears as it will be off. You will be running slower than your speedo states ( i.e. my astro runs almost 80 when I'm only going 70-72). I've never dealt with a tow button, but I would imagine it locks the torque convertor which would reduce on heat and maybe even prevent you from using OD. Best advice is to read your manual on that one.