I had a '99 2500 4WD with the big block Vortec 454 (7.4L) with 285/75/16 (~33") tires, and got around 9 mpg, but I have a heavy foot. It's possible with a higher lift and/or larger tires that you may see the same mileage or worse. I believe the front driveshaft on the 4WD models spins continuously, even in 2HI, which contributes to the mileage problem via drivetrain losses.
The 285/75/16 tires rubbed occasionally when turning into a big dip, and I don't think mine had aftermarket suspension (though shocks had been replaced, so could have been slightly longer than stock), though may have had the torsion bars cranked a bit. I think the 2500 & 4WD models sit a little higher, so you might just be able to stuff 33" tires in there with only occasional minimal rubbing.
With the IFS, they aren't ideal for hardcore wheeling, but mine saw plenty of fire road & normal 2-track use, with no issues.
The 96-99 got the Vortec version of the 454 and were rated at 290hp & 410 ft lbs. With an aftermarket air filter & Flowmaster 50 series exhaust, mine had a nice V8 growl, and was probably over 300 hp at the crank.
So with a 3/4 ton frame, big block engine & heavy duty 4L80E trans, mine had no problem towing a car on an open deck trailer multiple times (pretty close to the 5k towing capacity you are after), even with the cargo & seating areas loaded with cargo.
Over approx. 5 years ownership & 30k miles (75k - 105k), from what I can remember, other than basic service, mine needed a new transfer case not too long after purchase (probably as a result of not being shifted in & out of 4WD occasionally by previous owners to keep things lubricated), some plug wires, exhaust manifold gaskets & a starter, so not too bad overall. Edit: I think previous owenrs had front end rebuilt just before I got it, and I think I had some front end work done as well, and I think I had the power steering pump & lines replaced too.
I did many memorable trips in the 'Burb, all over the desert Southwest & down to Baja numerous times too, so was sad to let it go.
I replaced it because I wanted better mileage & to try a diesel, and after lots of searching found a good deal on an off-road prepared '00 Excursion with 7.3L PSD, but that's in a different price range than what you're looking to spend.
If the '99 big block Burb is in good condition, and you can stomach the mpg, it sounds like it would serve your intended use relatively well.
The 285/75/16 tires rubbed occasionally when turning into a big dip, and I don't think mine had aftermarket suspension (though shocks had been replaced, so could have been slightly longer than stock), though may have had the torsion bars cranked a bit. I think the 2500 & 4WD models sit a little higher, so you might just be able to stuff 33" tires in there with only occasional minimal rubbing.
With the IFS, they aren't ideal for hardcore wheeling, but mine saw plenty of fire road & normal 2-track use, with no issues.
The 96-99 got the Vortec version of the 454 and were rated at 290hp & 410 ft lbs. With an aftermarket air filter & Flowmaster 50 series exhaust, mine had a nice V8 growl, and was probably over 300 hp at the crank.
So with a 3/4 ton frame, big block engine & heavy duty 4L80E trans, mine had no problem towing a car on an open deck trailer multiple times (pretty close to the 5k towing capacity you are after), even with the cargo & seating areas loaded with cargo.
Over approx. 5 years ownership & 30k miles (75k - 105k), from what I can remember, other than basic service, mine needed a new transfer case not too long after purchase (probably as a result of not being shifted in & out of 4WD occasionally by previous owners to keep things lubricated), some plug wires, exhaust manifold gaskets & a starter, so not too bad overall. Edit: I think previous owenrs had front end rebuilt just before I got it, and I think I had some front end work done as well, and I think I had the power steering pump & lines replaced too.
I did many memorable trips in the 'Burb, all over the desert Southwest & down to Baja numerous times too, so was sad to let it go.
I replaced it because I wanted better mileage & to try a diesel, and after lots of searching found a good deal on an off-road prepared '00 Excursion with 7.3L PSD, but that's in a different price range than what you're looking to spend.
If the '99 big block Burb is in good condition, and you can stomach the mpg, it sounds like it would serve your intended use relatively well.