Friends car

I know this is really random, but i just wanted to see if you have any general ideas of what may be wrong with my friends car. my friend has a 99 GT that is i think a 35th aniversary. its a coupe that a guy had, then flipped it up on its side on a fire hydrant. so my best friend's (who now owns this car) dad owns a body shop, so they bought the car for i think he said 2 grand ish and then put about 7 into it fixing it. if that sounds wrong then whatever, the point is he had one that was wrecked, he bout it for cheap, then fixed it. they had to do allot of stuff to it to fix it too, like stretching the frame, and of course alignment and whatnot. the problem is that he thinks the guy that owned it before him put some kind of chip in it or magnaflows..., and he says he thinks it has 350hp. i know i know thats bull****, but he also says that it made it run hotter than it should so its probably around 300, after drivin this car, and riding around with him all the time, i can say that it would suprise me if it had 2 50 hp. i htink that theres serious problems with this car, and besides that i think he needs a new clutch. because one time when we were tryin to get down the road in a hurry, i felt his clutch kinda kick in and lock up even though i know he wasnt featherin the clutch and then realized it then took his foot off. this wouldnt suprise me either, because his mom drove the car before he got it and she kept her foot on the clutch a little, so there is so some slack in it. so what im asking is what can make a car run hot that can fixed in a driveway easily.. also does this sound like something that is common, im starting to get disapointed in this thing...mainly cause when he actually floors it we arent going much faster than i do in my moms cherokee when i floor that... if you have any ideas as to why this stuffs going on, then throw something at me. my only ideas are a new clutch and a lower temp thermostat. but i have no idea other than that any help at all would be appreciated. thanks.