New to me 2007.5 Silverado - So i have had this 2007.5 Silverado with the 5.3 for a few months now and really love this thing!! Had it since April ...

So i have had this 2007.5 Silverado with the 5.3 for a few months now and really love this thing!! Had it since April and the only problem so far is the check engine light came on and i had a buddy scan it and it said P0121 Throttle/pedal position Sensor A circuit range performance... This was on Saturday so right then i think i just need to spray a little throttle body cleaner in it and clean it up a little bit i have had a 03 envoy that i did before and it helped alot... Right after i did this i decide to call my local GM dealership and ask them how much the TPS cost (which i did not know you have to buy whole the throttle body for 272$) and the guy says he has sold alot of these recently and asked me if my truck was under 100k miles and informed me that i am still under powertrain coverage... I am the 2nd owner of the truck and when i bought the truck my dealer told me that there was no coverage left and tried to sell me one so i did not think i was covered the truck only has 55K on it... long story short i made an appt for monday at 9 am to take the truck and then when i put it back together the check engine light is only on when the motor is off and the key is in the on position which it never did before but not on when running.. Now i dont know if i should cancel the appt or keep it cause it will cost me 60 for diagnostics if they find nothing...
Also ever since i have had the truck if i floor it in any gear it wont shift till 6k RPM and it will even bounce off the REV limiter in 1st unless i let off a lil but then it will shift fine.. Does everyones truck do this? I have seen youtube videos and it looks to me like its supposed to shift at 5750K RPM.. Could the truck be chipped or something it will also go past 120 i dont know if theres a speed limiter stock or not i dont know anyone else with a truck like mine.

It could have a chip in it, which you'd probably want to remove before your trip to the dealer.

Good luck!

Check engine light always comes on when the ignition is full on and the engine isn't running. I wouldn't pay to have the dealler tell you that. As for the tranny issue, haven't a clue. Could just need a fluid and filter change. Any idea when that was done last ?

Have no idea when it was done or if it has ever been done need to do it soon as im approaching 60k... The check engine light now comes on every other day but turns it self off within a day im just waiting for it to come on while im by the dealership.. I have no idea how i would go about taking a chip off if it has one of how to tell if it does have one all i know is it shifts hard into 2nd to the point where i chirp the tires without trying and does not shift till 6000k RPM in any gear and will go past 120... Is there a supposed to be a speed limiter in this thing?

If the check engine light is on when the engine is running there is some kind of issue. Go to Auto Zone, Pep Boys, or the equivalent, and ask them to read your codes with their OBDII reader. They will also tell you what the codes are indicating and they'll do it for free. Then report back to the group and see if someone can tell you what to do next. If the transmission isn't changing gears it needs to be addressed. Could be a vacuum issue, low fluid, old fluid and/or a dirty transmission filter. As for a speed limiter, it could very well have one and it would certainly kick in around the speed you're talking about assuming the tranny is in top gear when it stops excellerating.