The symptoms of the problem might include rough shifting, shifting failure, an inability to downshift during aggressive acceleration, and otherwise. For unreliable shifts make sure to check on the transmission fluid level and given the right fluid type top it up. Check the status of the fluid; if the fluid looks dirty or has a burnt smell, change it as per the kind and quantity of fluid because it might be an indication of internal slippage and more future repairs. Check whether filler have been fitted incorrectly, whether there is no or inadequate filter gasket, if gaskets, pressure lines or fittings are loose or leak, and make the corrections. Also, check on shift or throttle linkages, or vacuum connections for breaks or slackness. If the transmission does not engage, look internally for wear on the shift linkage on the transmission and for a proper position and add any of the lost fluid. If linkage has been correctly installed the levels of fluids are satisfactory but the engagement is still unsuccessful then there can be internal damages in a case that requires disassembly of the parts. For down shifting problem during fast running check Computer Controlled Transmission for faulty sensors or control units and-check Kick down linkage or vacuum servo for their adjustment and for any leak. Electrical connectors of automatic transmission should be checked for security, cleanliness and absence of any damage on their end contact points but any cleaning solutions to be used on electrical contacts should be safe for use around the components.