I had the check engine light up a couple of times, checked for codes and came up with throttle pedal potentiometer so fitted new pedal assembly. , Now the car feels much livelier,,,,, any one have an idea why ? It seemed to run fine before even with the check engine light on

Old sensor pots not reading correctly against each other in the pedal assembly sensor, and was causing the problem.
Hence there are two pots not just one in the sensor, so when the two pots are not reading correctly against each other, this will cause problems.

Sometimes is just a mater of pulling the sensor apart to clean the bars on the pads and swiper arms, while on some sensors, the swiper arm are so end tips worn out, that you need a new sensor instead. As for GM, then only sell the sensor with the pedal assembly as a complete unit.