hopefully you're using the right gas in the first place.
If you're riding on v6 and using regular gas to save money, that might lack you from having proper power for your vehicle... and also if you have A/C running, that also take away some power from you engine. Not A lot but just enough where you can feel the difference slightly.
since it's 05', unless you drove it hard... shouldn't be from like spark plugs or anything. but it's not impossible either.