Both my father and I pull 25RR's with a half ton. I have a Ford EB with the 3.73 gears and my dad has a truck similar to yours. We have both added leaf springs to stiffen up the rear end and both pull the trailers fine (although I would argue mine pulls better than his does). We both load ours up with GL1800's as you would. At this exact minute, I'm not certain how much heavier the 27RR is over the 25RR but it can't be too much more. Personally, I wouldn't go much heavier than what I have now. I like having a ton of extra capacity left over with my trailer. I often load up the bed with firewood or other cargo. You'll also need a ramp modification on your trailer so your wing clears (but I guess that's another topic).
I hope that helps some. You will get varying opinions on weight on this and any other forum.