DS: If you look at the manufacturers information for towing ratings for the slushbox vs manual tranny scenario, I believe most trucks are rated for higher towing loads with the slushbox auto.
I test drove two brand new Ford F-350 diesels last weekend, one with the 6 speed manual, and one with the 5 speed auto. I too like the idea of a manual tranny as there is less to go wrong, but a manual coupled with a turbodiesel is a pretty clanky affair. These heavy duty manual tranny's don't shift like a Ferrari. Even if you don't use the lowest gear starting out, they are so low geared that if you want to make a quick left turn at an intersection from standing still, leave yourself LOTS of time. I was more than impressed with the auto tranny package, and for $1,500 bucks CDN extra I'd take it any day just for extra driveability around town in traffic. If you're on the highway lots, the manual would do you fine. Most times on the highway a turbodiesel is going to go up all the hills in top gear, unless you've got some real load on it, so you'd never be shifting the manual on the highway.
Keep in mind that oil changes with any auto tranny can be expensive. I drive an F-150 4.6L with a slushbox (auto) and my tranny oil changes are every 50,000km. Oil change cost is about $250 even at my brother-in-law's shop, as the spec calls for full synthetic lube. Even my little F-150 takes
12 or 13 quarts of synthetic lube and at $10 or $12 per quart it adds up quick Don't ever skimp on tranny oil changes and let Mr. Lube talk you into an in-place recycle where they tap into the cooler lines. Get the tranny and torque converter drained by a good shop so that they check the magnets in the pan for filings, and get that filter changed. My auto tranny is $3,500 bucks just for a rebuild, and its only in a little F-150, so don't skimp on maintenance.If you don't do much pulling I'd have to agree with Tom on getting the gasser. If you're just using the pickup to haul some concrete blocks, or dirt, or building supplies occasionally you don't need a diesel. If you do lots of pulling, the best gas mileage you'll ever get with a gasser in combined highway/mountain driving is 10 or 12 mpg or worse if your load is bigger. Where I live diesel is 10 cents a litre cheaper than 87 octane gas, and 20 cents a litre cheaper than high octane (94) which you really should have for pulling.
The Cummins diesels are awesome. My friend has a work truck for his business, a '90 dodge cummins with 500,000km on it, and it runs like a dream, with almost no repairs. A friend of my brother in law has two cummins dually's that haul heavy loads of passenger and heavy truck tires for a tire warehousing company day in and day out. Both trucks are about 5 years old I believe, and one has 400,000 km and the other about 500,000; and both are still running strong.
GH