The Proportional and Integral settings are part of a tuned system. You cannot just go in and willy nilly start changing and experimenting with random values and expect an improvement in your situation. Return to stock and do not touch them. Forget they exist.
You can look up a
PID controller to learn more...but this is just a PI controller...or
if the Derivative component exists, then HPTuners has chosen to not exposed it.
Proportional responds quickly to large errors. The bigger the error, the harsher the response. It's behavior is in proportion to the error...big error = big response.
Integral does not care about the size of the error, it only cares about how long the error persists. The longer the error = the greater the response. It is slow to react, but it adds more and more correction the longer the error persists.
So you can see there is a system of checks and balances going on.
During an error, Proportional (P) makes a quick change to knock the error condition down quite a bit. But after the initial error correction P loses interest and make less and less of a contribution to error correction...to the point that error correction is not going on.
It is at this time we expect a perfect hand off then to Integral (I) who sees the lingering error condition has been going on longer than expected and starts to work on it.
Derivative (D) then is the final check and balance to ensure we do not over or undershoot the collective correction from P and I.
So if you change P to be more of less active, then when you hand the error condition off to I...he is not going know how to correctly respond and end up over/under reacting and throw the whole error system management off. It is also important to understand that the [Total Error Correction] = [P] + [I] + [D]. So while I am making it seem like P works, then I, then D...that is not the case. All 3 (or 2 in our case) are active at all times working on an error condition.
If you change P then you have to change I. If you change I then you have to change P. And since this is a tuned system, you cannot arbitrarily change one and then tune the other. There is a very narrow set of acceptable values that works in controlling a system. To further complicate things, GM has added A LOT of other ancillary values to this PID controller (for under/over, max values, coast/idle, steps, etc). All these values work with the physical throttle body (diameter and TAC tables, etc).
This is a case of less is more, as in the less values you change from OEM the better.