From the information yo uhave given, I would say that the problem is electrical in nature. BUT, I would NOT say that the PCM is the primary suspect. As a matter of practice, the PCM is the most reliable part of the system, and the last to suspect.
Electronic systems are a bit peculiar in that the PCM needs to be satisfied that every other part is in working order in the system. If the PCM is not satisfied, it will go into a default mode or "limp" mode to get you to a repair facility rather than being stranded many miles from help.
Having said all of that, let's get to diagnostics.
Start by checking for codes. I would suspect that you have a shift solenoid that is sticking or intermittent. Once you have the codes, you can post back with the resukts, and I can point you towards the repair that is needed.
Sunday, May 31st, 2009 AT 8:36 AM