96 Nissan Maxima takes 2 to 5 min.@ 2000rpm to shift to 2nd & won't shift to 3rd

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Car has 220k miles, replaced VSS and fixed speedometer. Had CEL on before I replaced VSS. Now, no CEL. Autozone said I need a knock sensor and I had a code P0600? Besides the TPS, TCM, ECU, transmission shift solenoids, & cleaning throttle body any other recommendations? This is daughters car & I don't know how long & how far she has been driving vehicle with 1st & 2ng gear only. When driveing vehicle o/d button doesn't effect car at all.