I've taken it to a mechanic and he checked my computer told me it has been replaced once I gave the mechanic a spending cap and I still don't have my problem resolved wanting to do it myself but I'm stuck it was driving awesome and then all of a suden it wouldn't go past 60

Check for codes. The Transmission Speed Sensor (TSS), which may be failing, reports transmission output speed to the on-board computer. When not replaced, the transmission may not shift out of low and vehicle may experience inaccurate transmission shift points. Easy to replace. If not the TSS, I would suspect the Vehicle Speed Sensor (VSS).