Code p0300 already changed plugs and coils still has no power and idles bad took it to a shop they said cylinder 6 low compression

What is your question?

Have changed plugs , coils , oil and filter , air filter , vvt solenoid , the truck has no cat for what reason ( IDK) and i finally got to a shop and they looked at it for 5 to 7 min and brought it to me and said cylinder 6 low compression

What makes this problem better or worse?

When i put my scan tool in and delete the code it gets a little better

How long has your 2007 GMC Envoy had this problem?

I just got it a week ago the previous owner said 1 or 2 coils were bad and in need of a tune up