Not to repeat myself, but I've fairly new to the San Andreas game as i mentioned.
The thing I noticed about many challenges is that you need to finish some others before the game will let you beat a given challenge.
Take for instance killing Tenpenny's partner ( he goes from the ghost town behind the damn and drives towards San Ferrio;
I chased that guy with the sandrail till I was blue in the face to no avail - I hit 'em with rockets (nothing happened)Then I got the air field challenges finished (mentioned below), and just like that it was easy as a slice of cake.
I attempted to get on the plane at the desert air field several times and never got close enough to it to even think I could do it, but after I finished everything else well all of a sudden there was this sand storm to slow that plane down and I was on it in a flash.
I beginning to think thats why I couldn't get the monster truck thing done, but I attempted to do it again with the frame limiter and wide screen on but no dice
I've got 78.61 % finished
108 missions (580 tries)
cash 99999999 ( I like to play the horses )