2005 chevrolet Colorado 3.5 intermittent gas smell in cabin

You need to repair the exhaust/manifold leak. Possibly a blown gasket.

Call any dealership, they have to tell you truthfully if so

These should be labelled in the fuse block. If not, shop manual should help.

I had the same problem in the past. A mechanic told me that sometimes the keys become worn and will cause that problem. They made new keys and it worked just fine.

fuel pump turn the key one and listen if you can hear it come on if not its your fuel pump

if inded the smell of exhaust is getting into your car i would suggest not driving it until it is properly checked by a licensed meachanic. it could be entering through your heater/AC blower and in return be fatal if left untouched for a period of time

If there are no visible fuel leaks or check engine light on, with codes, the 2 most common causes are a plugged evap canister or bad canister purge valve.

Firstly change your cabin filter(s) if smell still present then there is a cannistor you can buy from AC speciallists. You open the canistor, leave in footwell, close the car (windows, sunroof etc) and leave for a few hours. The can lets off a special gas that kills bacteria caused by AC. Problem solved.

check the ground from the rear lights...

Sounds like it needs spark plugs and wires, and a fuel system treatment.