truck too heavy for 5.3?

I have a 70 3/4 ton crew cab short bed pickup, that weighs somewhere between 6000-6500 pounds. I am planning on changing to newer suspension and running gear. Will probably end up changing it to 1/2 ton.The truck will probably loose alot of weight, but will it still weight too much for a 5.3/4l60e? Will it be a dog, performance wise? Would like to be able to tow with it occassionaly. If I use the 5.3, I will probably get a Nelson Performance tune. I know on the last FSC i had, it helped out ALOT! It was a extcab sb and ran real well, so I'm currious as to how much the extra weight will affect it. Oh, and I am looking at the 5.3 because I have an opportunity to pic up the complete motor, tranny, etc for cheap. It's an 05 Tahoe motor and tranny. Is there anything i need to know about using this motor before I purchase it?

Thanks
Trey
<TX>

Never mind. I drug my feet too long and someonelse snatched up the deal! I'll just have to keep looking!

Thanks
Trey
<TX>

I think you should go 6.0 and 4l80e With 4.10s.......Go BIG or go home.