My Sidekick is a 4x2(sorry Guys) the plate inside says 35 psi for the 197x15 I'm running 215x15 do I run the same pressure as the plate says?

I go by the tire before the data plate.  Other people run 5-10% under the recommended tire psi.  Since you changed the tire size and they are bigger, just go by the tire. 

you shouldn't just go by what is written on the door or tire. I only run 20psi in my 30" BFG muds in a samurai SJ413K. It's not the best fuel milleage but I find it's the best drive.

One way to see what is a nice pressure is to find a flat road or parking lot. Get some sidewalk chalk and put a line from one side to the other. Drive forward and back 100' with no turning and no hard movement and then check the tires. When you find an even wear of the chalk then you've got the right pressure. gone inside then too much pressure, outside means too little pressure.

The front and the back probably won't be the same and when you add weight or tow then it might need some more air. In the summer when I go camping or haul some weight or long trips then I put it up to around 25 psi.

There are too many factors involved in all the different tires. Road tires, mud tires, radial ply tires. ...trial and error.

perhaps the data plate says max 35psi cold(mine does), but the recommended for my stock tires(205x75x15) was 23psi, front and rear.
i don't run stock size anymore, but look at the rating on the tire. it'll give a load rating at some psi. think about actual weight per wheel. do some guess math- it will be a lot less than the max.
example: my 31x10.5x15's- 2250lbs at 50psi- axle weight about 1500lbs or 750lbs per wheel = 17psi.
i actually run more like 20psi on the road(much less off).
did that make sense?
did some rounding, but .....
too much pressure gives hard ride and wears out the center of the tread.
too little gives a squishy ride and wears out the edges.
just my thoughts

it goes by feel too. When I bring it to the garage for safety they always load it up to 32psi and it turns real easy but holy man is it ever rough. They told me that I was crazy to run 20psi but they are not the one with a sore back.

25lbs in my doenuts anything higher i feel like a superball on the freeway,
20lbs better but harder to turn 30inchers w/o power assist.

You can put a chalk mark across the tread, drive a short way and look to see
when the mark wears away all the way across the tread width, as you lower
the pressure, this will be the correct pressure for the weight of the vehicle
and that tire size.

You might want to lower it another 2 PSI from that point to improve the ride
if you want, depending on your driving style and the loading of the vehicle

Wild

Tire manufacturers mark the tire with the MAXIMUM inflation pressure for the maximum rated load. Tire shops mostly don't know any better.  They do see a lot of tire failures from under-inflation and also have a legal concern -- they don't want to get sued.  You might be loaded to [maybe] around 40% of rated, so tire pressure should be reduced to keep the tread flat on the road. It is probably not a linear relationship, but the method presented earlier is a good start.  Seems to me that you should end up around 20-22 psi. You back will thank you.

Edit: My Samurai calls for 205/75R15 at 20 psi unloaded (but 26 psi rear when fully loaded).  It's on the plate at the left edge of the dash. I'm running 215's at 20 psi on the street and 10psi on the trails.