Power Steering issues......

I've replaced several pumps on my xj over the years. First the xj: 94 D60's, H1's and 42's with single ram hydro assist. On my last couple of trips I have noticed that the power steering will start to die and the pump will make noise. I have also noticed that after a break it will be fine. My first thoughts are to hot fluid. So a cooler was installed on the front of the evaporator in front of the radiator. This last trip pretty much confirmed its fluid still getting too hot and loosing its ability to assist. Let it cool some and it gets better. I have a couple things I want to try. The first is more flow. I have an old pump and I drilled out the removable high pressure fitting to 5/32. I know some have switched to the WJ pump. I am also considering a fan pushing air over the ps cooler too. Another idea was to relocate the cooler to the back or under the jeep. Any thoughts? Has anyone successfully used a factory pump with large tires? Or am I destined to a high dollar pump and box? Thoughts? Comments? Suggestions?

Even with a cooler, the small stock resi doesn't let the system hold a lot of fluid. Before I got my PSC pump & remote resi on, I ran the stock pump with the pump mods. It did okay, but it would do the same thing and get hot when it was getting worked hard. Adding the PSC resi doubled the amount of fluid in the system.