99 Won't quite shift into park... Help

I just bought a 99' Silverado off of my brother. When I got it, the shifter felt stiff, and didn't want to shift into the gears without pulling pretty hard on the shifter. I went to the store and came back and put in into park, and the indicator was stuck on R, but I hit the gas to see if it was in Reverse but it was in park. I shifted down and tried to put it in park again, and the indicator disappeared. I shut the truck off and tried to start it again but it wouldn't let me, so I put it in Neutral and it fired right up.

I asked my brother about it and he said it had always been like that. (He only had it for 5 months) I figured it just need greased, so I climbed under the truck and sprayed some white grease on the little arm that comes out of the trans. It helped a little bit, but still felt stiff. I tore the dash apart and looked very close at the shifter and the notches on it to make sure that they weren't bent or anything, and they looked fine. I unhooked the cable from the shifter and dropped the shifter into each gear to test it and it was fine. I hooked everything back up and crawled under the truck and unhooked the cable at the tranny and the little arm will shift through all the gears with one finger and it seems pretty smooth. I hooked everything back up and it will now shift into gears MUCH easier. All I have to do is pull the lever towards me and pull down slightly and it goes right into gear (Like a normal tranny would) But it still doesn't want to go all the way into park. The little indicator on the dash will move and sometimes stay on R when I think it is in park, and I'll try again and the indicator will just disappear. Sometimes it will go right into park, and other times it won't at all, and sometimes if I am on an incline the truck will roll just a little bit and then "pop" into park.

If it wasn't for the way the truck acts on the incline I would say that it is some type of sensor not letting the truck go into park, but with the way it kind of pops into park on an incline, I'm thinking something is stopping the cable from letting the arm go all the way into park.

Any suggestions?

I had a very similar problem with my '99 a couple of years ago. I took it to the dealership and they found the shift cable to be bad. It had a bend in it not allowing it to move all the way into the different gears. Replaced the cable and and problem was fixed.