Adding air decreases the rolling resistance thereby providing better fuel economy, but I don't want to exceed any safe limits.

I was running 33psi untill gas went over $3.00 per gallon and now I am running 37psi.

Whats a good safe maximum pressure to run?

The increased tire wear from the crowned tread will probably cost more than you're saving in gasoline, to say nothing about the teeth rattling ride.

In any case, though, TireRack has an easy way to find the max pressure for a specific tire (and they are different). Click on your <a href="http://www.tirerack.com/a.jsp?a=AR4&url=%2Ftires%2Ftirebran.jsp">Tire Brand</a>, then the Specific Tire, and then the Specs. For example, the max pressure for the Michelin Pilot A/S is 51 psi.