Is your truck a 4x4 or a 2wd?
I'd say at least 37s, but if it's a 4x4, maybe bigger.
As an example, here's my truck: (couldn't help posting pictures of my own
It's a 2000 1500 Sport model also, haha.
2wd, 3" body lift, 33" tires, 16" rims, and I think +2mm offset.
You'll want to go with the -12mm offset; that'll push the wheels and tires out away from the truck more.
I could probably fit 35" tires if I had a bigger offset, like -12mm on the rims you're looking at.
I'm recommending 37" since you're going will 4" more of lift than I am.
If you have a 4x4, you might want to even think about going a little bit bigger than 37" since 4x4s sit 2" to 3" higher than 2wds.