check transmission fluid then go to transmission mechanic. problem may be in computer and be a simple fix
It depends on what the problem is. From your question it is obvious you need to have it looked at by a professional.
Could be a transmission problem, assuming an automatic transmission.
There can be several things that will an automatic transmission not to work properly. The most common cause is a lack of transmission fluid. Broken shifting linkage can also cause the problem.
Problem with the transmission. You need to have the transmission computer checked for codes to know a possible cause.
That indicates a problem with your automatic transmission.
I had the problem on a 1994 with V6, sounds similiar. I think the problem stems from the safety locking mechanism that requires the brake pedal be depressed prior to shifting.
Is yours an autoshift, or a fully automatic transmission? With the autoshifts, the synchroniser has a bad tendency to go out because of improper clutch manipulation. This shouldn't be an issue with a fully automatic transmission, however, and if that's what yours is, the first two culprits would be faulty circuitry in the transmission computer, or poor coordination between the computer in the transmission and the engine computer (this was a recurring problem for Allision automatics coupled to Detroit Diesel motors). There should be a way of reading off fault codes from the transmission, but that's going to probably require you to go to a mechanic with the necessary computer software to do such.
Most cars this is not a problem, the engines are identical.
The transmission may need a flush and filter, or in my 92 accord I solved the problem merely by changing the transmissions computer.
The real problem is manually shifting from gear to gear with an automatic transmission. If you are referring to the automatic upshift, there may be a problem with the EGR system or vacuum system.
A systematic plan for the automatic solution of a problem by a computer.