Trans problem....

When parked on any kind of incline, if i shift into park, it wont click into park and it will start to roll away. i have to push the shifter up really hard to get it to click into park. Thing is, I took it to the shop and they lifted the truck with me in it. They did some kind of adjusting and it clicked into every gear, even park. I get it back to the ground and drive home and problems resume. Help?

Does anyone want to help me? Please help!

The cable needs readjusted

Thats what they did at the shop and it didnt work. :-(
Any other ideas?

It has to be adjusted while in neutral