The doors on my 1985 Chevy C-10 pick-up are extremely difficult to close. They require a real hard slam but usually still remain partially ajar. Anybody ever deal with this before?

 

Probably not aligned properly. Our brand new Ford Ranger passenger door does not close unless slammed, it is going back in for adjustment.
However after a long time (or lots of use) the door hinges can sag and cause bad alignment.
I am not sure how to align the door so wait for a pro opinion

 

Chances are you have 2 problems. The door hinge bushings are worn out and need replacing, and the striker is worn and needs replacement. Autozone and advance auto parts ahould have all these parts in their "help" section and it is not expensive or hard to repair.

 

The strikers in the door jamb used to have a plastic collar on them. I'll bet you a dollar that they're gone now. The "help" rack at you parts store sells them as does LMC trucks on the web. The last ones I bought through LMC were around $10.00 each, probably cheaper at autozone. Doors are probably sagging but new strilkers will help alot.
If you can find someone who's good at aligning doors on your truck, let me know. It seems that there is a bolt on the top hinge that's a real mother to get to.