There's an AWD axle shaft thread pinned at the top of the 4th gen section that has some good info. We found out that the 3rd gen rear axle shafts are the same as the short rear axle shaft on a 4th gen.
I'm just going to copy/paste a long reply to an AWD thread asking about how to identify an AWD, and I pointed out the differences between years and even between the 3rd gen system since some parts are shared.
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Correct on all counts! AWD was from 2001-2004 long wheelbase only. Multileaf rear spring packs that you can sometimes see in side pics or if they have a pic of the tires and you get a rear wheel pic, sometimes you can see it there. Interior pics, look for the absence of the traction control switch on top of the steering column bezel. There is a rectangular [ALL WHEEL DRIVE] emblem on the lower right corner of the hatch if the hatch is original. Flat floor with removable seats only, as the stow N go vans couldn't accommodate the drivetrain layout with the seat storage in the floor.
The VIN code will have a "T" as the 5th character to denote AWD, as "P" is for front wheel drive. 8th VIN character is the engine, and "L" is for the 3.8 V6 which is the only engine to be paired with the AWD in North America.
Do you want to get into year differences? Are you keeping your van in your sig, keeping for parts or selling to update? Some 3rd gen parts swap over to the 4th gen AWD. Rear brakes are the same. The right rear axle shaft is the same. The 2001 AWD used the same PTU (transfer case) as the 3rd gen AWD; 2002-2004 is same PTU EXCEPT the output shaft (to rear driveshaft) changed length. Transmission is even the same.
Other year differences, the 2002-2004 used the same propeller shaft, different from the 2001 because of that PTU output flange length difference. That makes the 2001 propeller shaft a one year part, so difficult to find a replacement for. Actually, replacement parts for this drivetrain are very rare, even more than the 3rd gen (no rear CV axles available). This might make the 2002-2004 more appealing, as there are more donor parts available. 2001-2003 I believe still used the old wiring that was very similar to the 3rd gen vans. In 2004 the computer system was changed and not compatible with earlier years. The flex plate and cam gear changed in the way they trigger the sensors (different notches or windows). The drawback is the new system cannot accept autostick like the 3rd/early 4th gens can. There are other engine differences too, like the 2001 having an aluminum intake plenum and matched EGR valve/pipe, where everything later had a plastic plenum and different EGR/pipe. 2001-2004 also suffered from a fuel injector wiring harness problem; radiant exhaust heat would destroy the wires/insulation and cause wires to short together, possibly ruining the engine computer (injector drivers fry).
There was some decontenting to save money around 2003/2004, such as power window switches losing their lighting, removal of one of the hatch/cargo interior lights, the windshield defroster for the wipers going away in 2003, and the taillights changing from 2 main bulbs per light to just one. If I knew all of this a couple of years ago, I might have passed on buying my 2004. I would have preferred a 2002 as to have the most features, best availability of parts and better build quality.
I got lucky when I was searching for a donor van for an engine for my 2004. I found a craigslist ad titled simply "Caravan $600" and I looked at the pics. It was a 2001 Dodge Grand Caravan ES AWD with leather and autostick! I drove it home so I know the condition of the drivetrain. 225K miles on it and all rusted out, but good engine/trans/AWD drivetrain and all the other electrical parts. I stripped everything off and scrapped the shell, so I got my value in spare parts. It's what made me research everything and learn all of this so I can help others. I plan to swap the engine, PTU, computer and all wiring to make it all work, including the autostick. I have 3rd gen AWD rear diff, torque tube/driveshaft, CV shafts and propeller shaft/VC assembly to swap in so I can manually lock the rear diff to the driveshaft for traction (or drifting) on loose surfaces. Might be nice to be able to back up in front wheel drive only in parking lots, and do away with drivetrain bind.
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How's that for a read?
I also got to thinking if it would be easier to put a 4th gen AWD system into a 3rd gen van, since it is much simpler and lighter? I think the wheelbases in the long vans are the same, as are some of the chassis crossmembers to mount stuff. The only two things that would have to be special mounted (by drilling holes in crossmembers and adding nuts) is the driveshaft carrier bearing and the torque arm mount. 4th gen AWD parts might be easier to find. Beware of getting a driveshaft from a junkyard though, as the yard usually bends them with the forks of the tractors they lift the vans with. I bought a few before realizing the U-Pull-It yard had bent them (at least they have good joints to swap over though).