Around here that is almost STD. I see many lifted trucks hauling 5ths. In fact my truck ('01 F350 4X4) came with 4" blocks from the factory and I run 33" tires with no problems towing my 33' and pulling the toys behind that.
I would tow a 30'ish 5th with a 6" lift and 35" tires, but would regear the diff. to get back to the right ratio for good towing performance. You also must get good tired that have at least the weight rating of your stock tires.
Not to bash chevys, but a 6" on a chevy isn't much taller than what I have now. I know because thats what I have been looking at to replace my current truck, it sucks that you have to lift a chevy, but they come from the factory as low riders!!!!
'01 F350 PSD 4X4 CC LB SRW, firestone air bags, bilstien shocks, superchips 60hp, 4" cat back exhaust, front end leveling kit, aux trans cooler
'00 315 wanderer, Honda EU2000