How do you know if you have the tow package on a 2005 gmc yukon xl?

For one thing, see if you have a transmission cooler.

It does have the transmission cooler, I have a travel trailer and someone told me if you have the tow package you have the electronic brakes and I was wondering if this is true?

I don't think that is the case. Try Googling your VIN number. There's a way of telling the options in the VIN.

Thank you I didn't thing that was the case either!!

That means including a hitch platform, trailer towing wiring harness, engine cooling capability, transmission cooling capability, and sturdy frame for mounting the hitch. In addition, in many cases, factory designers add or upgrade such things as the rear-end (differential) gearing to make towing less stressful on the engine and transmission. They also upgrade the battery, alternator, and charging system wiring to handle the added electrical load of the trailer's lights. Towing-capable circuitry is added to the vehicle's onboard ECM (electronic control module, a fancy way of describing the vehicle's computer) so adding trailer lights doesn't harm the electrical wiring and connectors. And finally, they often upgrade the standard shocks/struts and brakes to handle the added load and stress of towing. That's a lot of designing and upgrading! While it may sound very convincing, it's important to remember that not all vehicle tow packages come with all those upgrades. Some come with a portion, some simply include a hitch and trailer wiring package. However, most original equipment (OE) tow packages include some or all of the aforementioned upgrades