I bought a jug of autozone antifreeze/coolant. Is it okay to mix with the red coolant i have in the radiator right now?

No. Only use the Toyota Red and/or the Zerex Asian formula coolants. Do not intermix different coolant formulas.

Learning Coolant Fundamentals (http://www.machinerylubrication.com/Read/841/coolant-fundamentals)

Basically, green to green, red to red (orange to orange/red). Mixing traditional green coolant with the traditional long life red coolant will result in a gel inside your cooling system, so never mix those two coolant types. Now that being said, most of what is out there today is able to mix with either type, just make sure to look at the bottle. If it says "mixes with any type, any color", then you're good to go. If it doesn't, then make sure you put in the correct type or pick up a bottle that says mixes with any type any color.

http://www.tundrasolutions.com/forums/1gen-tundra/177790-which-coolant/?highlight=Coolant

This thread may shed some light on your question.

There's a wealth of information on this forum on nearly any subject you care to discuss. You just have to research it.

I just changed mine and used prestone 50/50 any coolant. The factory fill didn't look bad at all and the interior of the radiator looked great with no build up at the filler neck.