* Different U-joint sizes: The 2500/3500 driveshaft will almost certainly have different sized U-joints at the ends. These won't fit the output yoke of your 1500's transfer case or the pinion yoke of your differential.
* Length: A 14" lift drastically increases the driveshaft length needed. A 2500HD driveshaft, even if it *could* be adapted, is likely still the wrong length. You'll need a custom-length driveshaft made specifically for your lifted truck.
* Slip yoke/Double Cardan: The type of driveshaft (slip yoke versus double cardan) might also be different between a 1500 and a 2500. Incorrect driveshaft type can cause vibrations and drivetrain damage.
* Diameter and tubing: While the 2500HD shaft might appear larger in diameter, the difference is often minimal. The primary gain in strength isn't just diameter, but also material grade and potentially the number of tubes (one vs. two piece).
What you need:
You absolutely need a custom driveshaft built for your specific application. A reputable driveshaft shop will measure your truck's dimensions, taking into account the lift height, to manufacture a driveshaft that is the correct length and has the proper U-joint sizes for your 1500's transfer case and differential. They will also select the appropriate material and construction for the increased stress imposed by the lift.
Attempting to use a 2500HD driveshaft without professional modification will likely result in drivetrain failure, possibly dangerous.
