I had an '01 Burb 8.1L with 4.10's and 285's.....I believe stock tire size is 265?
Live on the West Coast and towed quite a bit up and over them there hills close by.
Actually did an 8000 mile trip out East and back with 3 teen boys and 8000lb trailer.
Never had any complaints about powering up and over the mountains.
Just found it's sweet spot RPM-wise and let 'er get me to the top....actually gained on a Duramax that had blown by me on the flats climbing Steven's Pass in Washington. "Pass him Dad! Pass him Dad!" "Nope, he knows," I said :)
You've got a great, comfy, powerful familly hauler, so I'd suggest keeping it and MAYBE consider a differential ratio change.
Just the 2 cents from a West Coast'er :)
Wish I still had the 'Burb.