I just found out that there is no need to make a new gamer profile. Just save in one of the later 12 save spots and start a new game and dont cheat that one until you unlock the achievements. Worked for me. Also, none of the car spawn cheats block achievements except the police heli one. That is how i unlocked "One Man Army", and " Walk Free". For some reason, on my cheated profile, It gave me the "Cleaned The Mean Streets" Achievement after it was supposed to be blocked by a cheat. Figure that one out.
