Do your research and figure out what you're willing to pay. Then go in and negotiate with confidence knowing that you wont pay a penny higher. Carsdirect is a great resource for setting an upper bound on the price. I wouldn't take that (or any other) price along with me while negotiation however. Your unlikely to walk away with a deal more than $50 better if you do that.
I think you can get a $500 over invoice deal any day of the week at just about any dealer in the country. It all comes down to you convincing the dealer that you will buy the car at YOUR stated price right then. If they dealer doesn't believe you're a real buyer, you're never going to see their best price. On the other hand if you act like an overeager idiot, they'll know they can gouge you too -- so don't do that either.
Just walk in, ask to be shown the car you want (it helps to know they already have it in stock -- do your research) and discreetly guide the salesperson to the exact one you want. If you do this right, he should still think that your just shopping. Take it for a test drive and then go in and make the deal happen.
Let him make the first offer. It will be silly. Follow his offer with the deal you want. On these trucks, I'd start at $500 under invoice. The salesperson will look at you like you're being absurd. Just tell him to write up the deal and take it to his supervisor. Make sure (at that point) he knows you're not interested in games or rounds of negotiations. It helps to act hurried. He'll come back with a counter (at least once). Stick your ground . He'll beg and plead for you to raise it just a little. Tell him it's your final offer and repeat that you need to get home (maybe start to stand up).
You should be standing ready to leave, when he gets back. Don't be suprised at all if he comes back and tells you he'll take your first offer. I've had this happen on several occasions. If he tells you flat out "No", then you're probably not close. If he still wants to talk, then you can decide if you want to raise your own offer $500 or not. Don't do this more than once. If you don't make a deal, walk slowly on your way out. I actually had them rush out to meet me at my car before they'd take my deal once.
Make sure you know the complete invoice and all fees that will be charged (to the penny) before you ever step onto their lot. That first offer you make will signal to the sales manager that you've done all of your research and that you're working with all the same numbers that he is. He will do the math (backwards) and see that your number is EXACTLY $500 under their invoice and will be stunned and curious as to how you came up with that number. Don't bother explaining it to them. They'll just use the details of anything you say to work against you.
So your offer looks like this.
Precomputed Invoice cost - $500 (or whatever you want)
+ 45 doc fee (never pay more than this...it's pure profit)
+ CA license fee (something like 1% of deal cost -- look it up at dmv site)
+ 5 tire fee (yes you have to pay this in CA)
+ CA use tax (same as sales tax in the city you will garage the car in)
- Rebates (yes rebates are subtracted after tax in CA, not before)
- trade (hopefully you're not trading)
Your invoice cost should be (nearly) the same as what you'll see on Edmunds, cars direct, kbb, etc. You have add the destination fee. There are also a couple of other small fees that all Toyota dealers in SoCal pay. Search for the post about my deal last Februrary. It has all these details.
Good luck.