Hey guys I'm in the process of changing my gears in my 99 gmc. It's a 99 gmc sierra 1500 base model. It had a 4.3 In it when I got it. I'm wanting to go to 3.73 to 4.10 or 4.56. My question is exactly what gears do I need.ive found many different gm ones like 7.25" or 8". How do I determine which gears I need front and back?