Hopefully the OP isn't trying to build a 450hp truck with great gas milage.

I can get 22mpg on the freeway doing 80 with my 408 but city milage is ****

 

WOW....slurp slurp...well the way I see it, I dont think any truck gets good gas mileage what so ever. If anyone is really worried about that then they need to get a Prius. It runs off of strawberry douche. BAHAHAH!! Yea and thanks for the cooling system thing. I guess I have pro's and cons leaning both ways on which block to use. It seems to be that a well calculated price list might be the deciding factor after all of these responses. But if its close then Im sure I will just buy the 6 block. Either way its going to cost a lot. I told my wife Its going to be a snitty Christmas!!! Dog House

 

You can find 6.0L for a lot less than 1200. Just keep your eye open

 

Well, I filled out a form and every junk yard in the country is calling me. The one I have my eye on came out of a 2001 silverado 2500. They are saying it has 54K miles on it for $1,100.00 shipped to my door. I believe they are up north. I figured shipping from there to Louisiana wont be cheap. Prob around 4-500. So that would put it around 5-600. Im just basing the shipping on a trans my son had shipped last year that cost 450. I havent found one around here I could drive and pick up yet

 

'00 Sierra ECSB, 9.9:1 forged 6.3 (383ci), Magnusen 1900 (2.7" pulley, 11psi), I.W. 8-rib, Holley 90mm, 228/236 551/551 116, Crane 1.8 rockers, Patriot 243's, 4L80E, Circle-D 2600, ARH 1 7/8" + 4"

So Im guessing the 4L60E didnt hold together? Im on my second rebuild on the trans With 200,000 miles give or take a thousand miles. The first rebuild lasted 11,000 miles. 3-4th exploded the guy said. It was in pieces. I floored it coming around a corner getting on the interstate and it shifted to third then the rpms pegged out and I was going nowhere. Had to limp back 10 miles in 2nd. going about 35mph. This new guy I have to do trans said that they are just to delicate. Better off with a 400 but then he said Im giving up the 4th gear. I dont know. I just bolt them in and tear them up. As far as knowing anything about them Im dumb as a box of rocks.