Jack,
Welcome to the club.
Sunlines were just plain well-built compared to every other TT out there. Better design, better materials, and better workmanship. That's the magic.
Now, about your tow vehicle... First, which Expedition do you have? There are 3 possibilities according to the '99 towing chart:
Hopefully, you have the 2WD version which is rated at 8,300# max trailer. (I've outlined that version and the required options in red boxes.) There are a lot of other variables such as the weight rating of your axles and your weight distributing hitch, but let's concentrate on just the base vehicle for now.
Your T-267SR is 5,730# dry (empty) weight. It has a Gross Vehicle Weight Rating of 8,600# and a unloaded hitch weight of 750#. The GVWR includes the dry weight plus all the stuff you might put in the trailer like clothing, food, bedding, etc., etc., etc. That includes the possibility of all holding tanks being full plus a full load of propane.
Your TV also has a Combined Gross Weight Rating which is the max. allowable total of everything: truck, passengers, stuff in the truck, and trailer fully loaded. You will have to look on the door sticker for your particular truck to get the CGWR and the max axle ratings.
One other issue that is most likely not is your favor is the shorter wheelbase of the Expedition compared to pickup trucks (or even the Suburbans and Expeditions.) Again, most of us are using the extended cab models which give a long wheelbase even with a shorter pickup bed. When it comes to controlling sway, part of the equation is the wheelbase. Longer is better with the heavier trailers. The bigger the dog, the harder it is for the tail to wag the dog.
Conventional wisdom in the travel trailer world is that your tow vehicle should be able to handle at the very least 110% of the GVWR of the trailer without exceeding any of the ratings that I have mentioned. If you look around sunlineclub.com a bit and read some of the signatures, you will quickly notice that almost everyone who is pulling an SR is using at least a 3/4 ton pickup or SUV (meaning the 3/4 ton Suburbans or Expeditions.) There are a few using the newer 1/2 ton pickups that are rated up around 9,800# max. trailer weight, but most have opted for the heavier-duty everything that comes with the 3/4 or 1 ton vehicles.
You asked for opinions, so here's mine. If you have the Expedition that rates at 8,300# max. trailer, you are slightly under the base guidelines that I outlined above. It is my opinion that with a properly set-up weight distributing hitch system including the dual cam sway control system (or a Hensley), you will be able to pull that trailer. But, you will not be happy with it's performance on anything other than flat roads with a tailwind. And, the weight of that trailer will likely shorten the life of the Expedition especially given its age. Even if your truck is rated to tow 8,300#, you are right on the edge of overloading it.
If you have either the 7,900# max. or 7,400# max. versions of the Expedition, I would have to offer that I think you are too far under the numbers to tow safely.
Even if you have the 8,300# max. version of the Expedition, the rear axle ratings also need to be examined closely. With a 750# dry hitch weight, it is easily possible to reach a tongue weight of 900# or more when loaded. I suspect the rear axle is not going to be rated to deal with that kind of weight.
If you read some of the recent posts here in Introduce Yourself and over in Towing and Tow Vehicles, you'll see that a number of other folks have asked the same question with different trailer and tow vehicle combinations. The advice offered to each of them is all based on the same guidelines as I have outlined here.