Subject: Transmission shifting
Question:

I have a 95 Diamante Dual overhead camshaft. Automatic Transmition.
The problem I am having is the shifting, once I start putting gas to it it goes well, in the second shift the RPM goes down as normal, but immediately goes up and down once it shifted. Same problem as my third shift.
I am thinking that is not shifting properly and the RPM going up is because is idling and not changing gear.
Answer: Andres,
The first thing you should do is take your car to transmission shop and have them flush out your tranny fluid and replace the filter. Have them clean the oil pan and refill it with the proper fluid. If that does not fix your problem, the tranny shop should inspect the transmission itself. It may be as simple as a bad linkage or dirty valve body, but it could be as serious as requiring a full rebuild. But have the tranny fluid replaced first because it's much cheaper and should be done every 60,000 miles as regular maintenance.
Good luck!