Its probably the bottom latches that are stuck. If thats the case, you can take the door panel off from the inside if you havent already and spray the heck out of them with some rust breaker. Youll be able to see how the cable lifts up on a lever to realease itself from the latch. Try to get something in there you can use for leverage to help the lever along. You can even try having someone hold the door handle open while giving the door a little persuasion with your foot from the inside. If you have the door panel off, youll only be kicking the sheet metal so you cant really hurt anything. I helped my friend get one on his truck apart that was really stubborn but its been so long ago, I cant remember what we ended up doing right off the top of my head. Let me think on that one Ill give him a call tomorrow and check back.