Hey im new to this forum,and just wanted to ask for some help/ideas/questions.I have a 2001 Pontiac Grand Prix GT.Ive had this car for over a year already and its my first.It has been clean on the outside especially since I wash and wax it every week or two.However I have spent thousands fixing it up and many trial and error situations.You name it and it has been repaired from tranny rebuild to heads to brake booster and other brake work,batteries,starter,air filter,tires,upper intake manifold,etc.In all ive spent maybe 4k and now it appears I need my CV boot replaced,front and rear rotors,wheel speed sensor(ABS and Low Trac Coes on sometimes)and now even my cat.The car currently has 120k miles and I dont want to get rid of it because it has so much potential,but all of these arising problems and money being put into it every time is annoying.I wanted to start modding a while ago but since one thing after the next and not much money to work with right now,its hard.Is this really my cat?When I start up the car it sounds as if it wants to mis but it just idle/skips til its warmed up.Then as Im driving and around 50mph or 3rd-4th gear,as I accelerate at least half throttle the car sputters and lags acceleration and its hard for me to go faster.Whats up with that?My engine light is on nd the code says catalytic efficiency below something like that.What are good cats?magnaflow?And what are some basic cheap mods I can do myself that will give me some noticable gains?sorry for the long post just want to hear from experts/experianced Grand Prix owners.