Regarding the 'Hunted' mission - here are what worked for me in Feb 2016.
I'm using the 1.2 ver trainer as others also said. The others were crashing the game.
Dogs. Frustrating. I found the easiest way to deal with them is just to shoot them. The game likes to suggest that you Melee them and grab them by the neck. Pftthht. Shoot 'em. You might also need to disable the trainer options if you have problems with the dogs.
Stinger. After reading suggestions here, Googling every thing I could find and trying these with the trainer active and all options disabled multiple times, I finally played up to the Stinger section then disabled all three options just before Price told me to use the Stinger. Then, finally, the Stinger locked-on to the chopper and I was able to shoot it down.
The game is now several years old but it's still a hell of a lot of fun. Anyway, I hope that helps somebody as getting past that level can be a real PITA.
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