I've got an 01 expy with the 3.55 rear gearing, HD tow package (which is included with the eddie bauer option at least in 01).
My setup is similar to yours and my trailer is about the same weight and a bit longer. Horsepower drops with mileage as things wear so at 231k I'm sure I'm down 30% from new in the power dept.
My trailer tows beautifully - no sway, no bucking, no issues. Powerwise, since that is your question, is adequate. Now we had the trailer (5465 factory weight on the door sticker) with mebbe 800 lbs of cargo, if that - I kept things light on purpose (and I'm sure it won't stay that way
) and in the truck we had 600lbs of people/pets and 100 or so in cargo. The hitch isn't light. I'm guessing we're right at the 12,500 GCWR the book says I'm allowed (for a 4x4, 3.55 and 17" rims).
We towed it ~80 miles from near the ohio line on the PA turnpike into the allegheny mountains and while i'd love to say we had plenty of power, based on towing smaller loads in the past, I'd say we had adequate power. I'm used to barely knowing there is a trailer back there and with our Grey Wolf you know you're not alone.
What that means is there were a couple of hills where I had the pedal to the floor and the truck was shifting into 2nd. Now I never fell below 50 mph and when held to the floor we'd always accelerate back up to 60-65, and I did pass a couple of cars on one up hill grade.
How 3.31 gears would affect this situation I'm not sure, but if you've got a lot fewer miles you'll have more power so it may balance out.
As long as you're not trying to beat the clock I'd say you'll do fine - there really is no sure way to know until you do it, and you're threshold for speed/power may be higher or lower than mine or any other posters here.