RE: JR Z590M servo????
Yes, I have had a JR Z590M servo in my 4.6 SS for 5 gallons. Actually worked pretty good but there were times when I could tell it was not holding the wheels turned all the time. Especially with Big Joes or a larger diamenter tire.
However, overall, it worked just fine. This week-end I switched over to a Hitech 645 MG servo just for the fun of it. Maybe the Hitech is a little better, but not by a whole lot. So, from my experience the JR is Ok, the Hitech is a little better but neither really move the front wheels the way they should to be perfect.
Dennis