You will not have a problem mixing Mopar Power Steering fluid and ATF+4
Here my post from a few years back on that very subject.
In my experience you will be perfectly fine with ATF+4.
This is the experience I base this statement on.
I was working at Chrysler’s Desert Proving Grounds when the switch was being made to use ATF+4 all in power steering systems. We ran full durability tests using ATF+4 in the power steering systems on a number of vehicles that previously called for Mopar Power Steering fluid. For example, I remember 6 mini vans that were running power train durability.
2 vans used the then spec’d Mopar Power Steering fluid, two vans used ATF+4, and the remaining two used a 50/50 mix of the two fluids. The 50/50 test was to simulate the wrong fluid being used to top off a system. There were no issues with ANY of the vehicles. I don’t remember if temps were taken. But I know that oil samples were pulled post test and that the steering pumps and gears were returned to the proper departments for tear down.
There was a similar test run on vehicles with recirculating ball steering boxes and I never heard that there was a problem during or post test.
I personally changed my 2001 Dakota over to ATF+4 and could notice a reduction in pump noise. I had the ATF+4 in my system for well over 100K miles.
Jerry is correct in that we need to pay attention to what fluids were spec’d for our particular year vehicle. But in this case I wouldn’t worry about your use of ATF+4.