I bought a SR5 back in April with fairly low miles, 64,000. The rear end seems to sag with any sort of cargo or passengers in the back, any tips on how to fix this; add leaf springs, new shox, any input would be appreciated.

4Runners are famous for butt sag. Adding leafs won't help, you have coil springs. Shocks control rebound, not ride height. You could add some coil spring spacers, but the real answer is new coils.