i have oil in my radiator and ive checked the oil cooler. is there any other possibilities that i should check before checking the head gasket??

If you checked the oil cooler and its good then yes its a head gasket...

To do the head gasket you need clear bags so you can lable the stuff and put it back in the same place. Start off by putting the windshield wipers all the way up. The rubber gromits under the cowl are so you can get the push rods out and the wiper motor arm will be in the way. Drain the rad and wile it is off put the lower hose back on and get some dawn dish soap and squeeze it in let it soak with hot water. Put some in the heater core and back flush it. Then pull the return line off the back of the head.Remove the valve cover, injection lines, cross over tubes, injectors. start on the front head put every thing in a bag and mark it 1, then 1 intake, 1 exhaust, etc Get a cherry picker on the back of the head is a factory hook ring the front one is by the thermostat. I am sure i am forgetting something. If you want to call me i can talk you through it. It just takes time.

Its a time consuming job, it wasn't too bad! Did mine a few months ago. Now would be a good time to replace injectors and connector tubes