You should add a signature to your account with the year of car and maybe some of if any mods, or stock parts. What size tires your using has an effect on when you run out of gear , but I doubt that's what is happening . You could have a faulty ignition coil that breaks up at high rpm. You could also have a weak valve spring or springs causing valve float , also possible that your fuel system falls out at high rpms ie weak fuel pump , partially plugged fuel filter, old or worn out injectors. There are just so many possibilities .
You say your buddy messed with your timing , but do you know what he set it at ? If it was advanced to far you might be experiencing some pinging and loss of power.
Does it feel like it runs out of power in other gears? If your have stock heads and stock headers they greatly limit your rpm/power range. The engine simply runs out of breath.