Jody, your problems can probably be resolved by applying a little bit of lubricant to the shift mechanism. IT is possible that due to sitting for 3 months, the internals of the tranny has dried up. But, there isn't much that you can do about that without getting a small hose inside the tranny and spraying some lube around. Driving the car should do that though too.

As for the shaking that you are seeing, I would be looking at the centering bearing on your car. If you look at the driveshaft, at about where the front seats are, you will see a bearing attached to the body of the car. It sounds like this has dried out and is now rubbing, leading to your problems. Not a hard fix, but does require pulling the rear driveshaft.

Something else to consider is are you running bias ply tires? These are known to flat spot over time if they are not rotated and can result in the vibration that you are feeling. But, having a set of bias ply tires these days is hard to do as most tires are radial tires.