You can still get the manuals in chevy trucks today. It's the "new" ones coming out in 2007 that won't have manuals available.
Why wouldn't I want an allison. The question should be, why would I want an allision. Umm..well, from things I've read they've been plauged with problems from the get-go, with a boatload of the early ones flat out blowing up from the inside out, probably better now. Mainly it's price. without looking, I think it was a $2300 (a $1200 option, but then if you pick the 6sp you get -$1100, so effectivly $2300 to have the allison) option. That's way too much for what it is. Plus, I just can't stand automatics. They are never in the right gear for what your doing, they are still unreliable at high mileage. They are expensive to fix and replace, a clutch job costs me $500 installed, or $250 if I doit my self which I usally do. It takes a garage full of special tools and many hours of special training to build an automatic, and if you take it somewhere, watch out, for that trans in that truck, your looking at $2500 minimum. My SM465 in my '73 had 289,000mi when I tore that truck down for frame off. All it needed was a new input bearing and I replcaed the shift fork because it was cheap and it looked a little worn. New seals, and good as new. $100 in parts. My NV2500 in my '97 6.5TD has 170k mi, do I worry about it, nope, just don't hear the stories of them breaking. Autos are always hunting around if your not at the programmers speed and engine rpm points, you can't get the thing to do what you want. I just hate it. Just my opinion of course, but I think auto's blow chuncks. Every one I've ever had has been the cause of scraping the vehicle it was in. Th350 in my '78 k5 decided it was going to shift into first at highway speed one time, blew my motor (and trans). My wifes old' '94 dodge spirit trans blew up three times (the last time so bad, it's parts blew a hole in the side of the engine block) (that was the infamous dcx a604 or 41te trans), my '79 sunbirds trans blew up and cost more to fix than the car was worth. Plus I just can't stand driving them, it's annoying. Ok, so I think you all get the point, I hate autos. Not to bash those that like them, if you like them great get 'em. It's for you. I just think the automakers should offer the choice. And no manuals definatly means no new GM trucks for me after 2007.