I know the 5.3 is the way to go, but I found a great deal on a '05 Tahoe, only problem is that it only has a 4.8L in it. It only has 32,500 miles on it and they want $14,000. It even has dealer records...
I had a '98 Silverado with the 4.8 that towed my SAN like no ones business, made me really unimpressed when I got my '05 6.0, could barely tell a difference except the pump when the 6.0 burned a lot more fuel.
I have an '04 Silverado with the 4.8 and it tows my '02 Supreme V220 pretty good. It only struggles going up a grade of 6% or greater, but most 1/2 ton trucks have that issue.
If possible, check what gears the vehicle has. If they are 3:42 gears, then you will labor around, while towing. . . if they are 3:73 gears, you should be fine. I don't know if they offered the 3:73 gears with the 4.8L engine, though.
Like everyone else said, the 4.8L shouldn't give you any problems. I've spent a lot of time towing a 2005 Mobius LSV with a 4.8 in a Silverado and it did just fine. And that was in East Tennessee with lots of hills.