The rears on the Colorado are beefier than most think. Seen a lot take more abuse than the Silverado's rears, all other factors aside. I own a GMT900 and a 355. A swap is not straightforward at all. I've got a list of things needed in some thread here. Lots of cut lines to compensate for length needed, you can use the stock trans, just need a new input shaft and bellhousing, Current Performance makes a nice wiring harness, need a gas pedal out of a TBSS or other vehicle that the swap motor came from, etc. etc. etc. The list goes on and on, and it's not exactly a piece of cake. An 8.1 is absolutely stupid. There's more room in the engine bay than people think, but I'll just leave it at the fact that you should go with a typical LS with the stock trans. and the rear is good to much more h.p. than you might think. I'm just rambling about what I figured you needed to know by your questions, so if you want to know anything else, I'm almost 100% positive that I got it covered.

Gears, gut the primary cat, good exhaust, intake, and a 100 shot with a good tune. He's done. You know how these motors treat you on nitrous. :cheers:

Id 6.0 swap it...bolt on and DONE. Itll be wrecked in no time anyways.

well, with enough effort ANYTHING is possible ;)

hell...if you wanna go retarded do a duramax swap...

Really...do a 5.3/6.0 swap and go fast bud.

thats like saying i have a big dick and it doesnt work

i woud go with an alumnium 5.3 or ls1 insted

Hey I say go for it, but i wouldnt use the allison. I have an 8.1 in a 1500 silverado

4l80e

I'm with him^. Try to go aluminum if you can. Your looking at saving around 75lbs over the iron 5.3 if you were to go with an LS1 and of course the added cubes.