Current sensor with instrumentation amplifier (LT1167)
[This started as a comment, but I've run out of room.]

First of all, Welcome to EE.SE.

Second, I'd like to comment against the voltage dividers at the inputs.  Suppose, the resistors in the dividers are 1%, then voltage difference caused by the mismatch between the dividers will be comparable (not much smaller) to the voltage drop across the sense resistor.  You can test this hypothesis by connecting the high sides of the voltage dividers together (i.e. shoring out the sense resistor) and observing the output of the InAmp.  

Another thing to try, is to test your InAmp circuit without the dividers.  (V3 would have to be set to a lower voltage.)

Typically, high-side current sensing in a situation like this is done with help of a current mirror IC.  See this application note, and another one.