How far was the key hanging down/out of the crossmember unloaded? The stock 2500 keys should be just about level with the bottom of the crossmember, and are very easy to load up and put the keeper in. 1500/ lift keys for you, will hang down a quite a bit from the torsion crossmember, and be much harder to load up. from my experience, cranking a 2500 with factory keys will net about 1.5" of lift. with 1500 or lift keys in a 2500, you can go from about 2-3.5" of lift, or however far till it touches the droop stops.
I was just under my friends dmax yesterday and removed a broken adjuster bolt, so I'm pretty sure on how far the stock keys hang down.