We just bought a 23' Jayco Jay Feather TT (4700 lbs dry weight) and we currently have a 2003 Yukon XL, 5.3 L. I'm really struggling up moderate grades and based on all my research, I'm finding I need a 3/4 ton model. ...
I think you hit the key with the bolded statement. Get buying.
Okay back to what you asked (response based on 50 years of towing - others may well have differing and equally valid thoughts - and likely stuff you already know):
Towing is about horsepower, braking, stability, reliability (not necessarily in that order)
First define "struggling". Normal steep highway grade is 6%. How fast are you trying to go? What gear are you in? The book for my 99T says to stay out of 4th gear when towing - lets the engine turn up and run easier.
The answer could be to slow down a bit and gear down a bit.
So, does your rig have the factory towing package? What is it for towing capacity, gross vehicle weight? If it came with the towing package, the gearing is likely fine. Should be 3.42 or 3.73. The glove box options list will tell you. If it is higher geared, you likely are struggling. Doesn't mean you can't do it, just have to change your driving strategy.
What is the Hp rating for the 5.3L engine? For a gross weight of 11,000 lbs 200 hp is about the minimum - and it would have to be geared right.
Now about the new truck with more horsepower: Generally speaking, concerning towing, more horsepower is better.. How much is too much? When feeding it bothers you.
Consider, todays semis have maybe 400Hp. They pull 80K up 6% grades at 45 mph. Of course they have gears that will set the engine right at the center of it's power curve. And the engines are rated for 400hp continuous.
And we don't have that. Our gas engines are rated for maybe 50 hp continuous with bursts to 200Hp for 20 seconds while passing. The trucks are designed to pack the wife, kids, dog to the store and back. We are demanding 150hp continuous, and we want it reliable, and we want no more than normal maintenance.
So, I've got a 99T with a 5.7L vortec, 3.42. I am still setting up to tow, but my expectation is it will handle a 6000 lb cargo hauler with one passenger, and 250 lbs additional load. By handle, I expect it will do 60 mph on the flats, 50 on a 6% grade (45 will be okay), and 35 down hill on an 8% grade. If you want faster, you will need more horsepower and better braking.
As for "I'm not sure I want that much horsepower when I'm not towing" - raise your right foot. They don't exactly come with a switch that says "Tow - Store"
A half ton with 250hp, geared right, sprung right (tow package - for example) should perform fine towing 5000 lbs (11,000) gross. And, yes, the transmission is likely the weak link. I went with a bluetooth obd ii scanner linked to an Android phone to monitor the transmission temp. If we are in the hills, I'm keeping my eye on that. But even if we had a 4L80, I still would be easy on the transmission.
There is nothing wrong with wanting more. Even with more, you may figure out to pull into the truck lane suck up against the semis and climb about the same speed they do. And go down about the same speed they do. We finally did.
Enjoy the ride,
ice
