battery crapping out

just replaced the flywheel and starter in my truck and now its having trouble turning over and the battery drains very quickly. its a 1987 dodge ram with a cadiliac 500 in it. it cranked fine before the flywheel went out.

either the alternator is shot or there's a loose connection on it.

Did you torque the flywheel right? It may have a slight bit of distortion in it whitch puts more strain on the starter. I would check for loose connections like said above before anything else though.

Lets assume your battery is good (you have had it tested, right?)
I would suggest 3 things....

1. your starter may not be shimmed properly, causing gear to gear binding. Adding a thin shim or two between the starter and the block might help.

2. Your starter armeture bearings are worn or incorrectly assembled, allowing it to drag on the inside of the starter housing..

3. Your ignition is too far advanced, either too much static timing or the distributor advance weights are stuck in the 'advanced position'.