If you have a TGraph, SetRangeUser will not work for the x axis.
TGraph* myGraph = new TGraph(); ... myGraph->SetRangeUser(lower,upper);
will not complain but also not do anything. Or not the thing you want.
You have to use SetLimits(), like:
TGraph* myGraph = new TGraph(); ... myGraph->SetLimits(lower,upper);