So my "CHECK GAS CAP" light keeps coming on any suggestions on why. I've replaced the Gas Cap. It went off for like a week then came back on..................

It actually doesn't mean that the gas cap is definitely the problem--but is easy enough for the average person to check.

What the message means is that the EVAP system has a leak.
Sometimes the filler neck gets rusty enough to fail to seal.
This could be a failed purge valve, vent valve, bad line, fuel tank pressure sensor, damaged charcoal canister, etc.
The purge and vent valves are operated thousands of times, so they do eventually wear out.
Stick with ACDelco OE for the more reliable replacement parts.
Rockauto generally has good prices--and their Pontiac Bonneville Club Vendor's forum post offers you a discount code

Your car only does a leak test of the Evap system while the gas tank is between 80% and 15% full and while the coolant and intake temperatures are within certain ranges.
The EVAP test isn't run if those conditions are not present--making you think the problem was resolved, even when it wasn't.

Okay so out of all those that you mention which would be the cheapest and which is the most expensive to replace I recently replaced my fuel pump within the last month actually

Did you DIY, or have a shop do it? If the Check Gas Cap light started coming on after you did the fuel pump, I'd investigate the seal on the fuel pump assembly. Seems a little too convenient to not be correlated.

_________________
Bye Bye:

RIP sandrock

The light came on maybe two weeks later