I have a 2002 Pontiac Bonneville with 105k miles. The engine is getting poor fuel economy and struggles to accelerate but does not throw a misfire code or any other code. It also runs a little cool around 177° when moving.

Maintenance wise I changed all spark plugs, wires, coils, and module over the past year, the last coil was 2 weeks ago which fixed a steady misfire problem. I then started having intermittent misfires that would come and go so I suspected the injectors. I ohmed out the injectors and they were fine and changed the fuel filter since it was long over due after 40k . Now I don't have misfires just poor performance. Any thoughts?

Thanks in advance!

I'd check all the vacuum lines and where they attached. The lines or the posts they attach to may have gotten cracked.

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A stuck open thermostat will reduce gas mileage and will cause the engine to run cooler whenever the car moves.
It's a cheap enough fix but may not be the entire problem.

Have you checked the fuel pressure?
These cars need a rather high pressure
Be sure to check it at idle, at higher RPMs and then check with the fuel pressure regulator disconnected (should increase by 10 psi or more).
While my fuel pump was failing on a 93 SLE, it threw no codes at all--but began hesitating badly, and later, stalling.

This offers a number of useful ideas--including the one to change the 0 2 sensor after 100K, as they are actually maintenance items and that is the replacement interval.
http://www.aa1car.com/library/poor_fuel_economy.htm

Let us know what solves the problem for you.