Rpm gauge bounces up and down between 2nd and 3rd - jerks car forward but shifts fine after 3rd and drives as it should. Doesn't do it all the time. Any ideas as to what could be the cause?
It is hard to diagnosis the problem without me being there on the test drive.
When was the last transmission service performed on the car? How many miles on the engine and transmission?
Having a transmission service can help renew the fluid and increase fluid flow by changing the transmission filter. When the mechanic lowers the transmission pan he can observe the bottom of the pan to see if any metal or clutch material is in the bottom of the pan. This can be an indication of a transmission failure.
If the problem continues a test drive with a scanner (not a code reader) and a mechanic who can read the data on it properly can be a big help because the scanner can supply the input of all the sensors and switches of both engine and transmission and also supply trouble codes so the mechanic can analyze all the data and determine the proper area to look into.
Having a good transmission mechanic can help locate the problem and hopefully it can be repaired without taking out the transmission. This could be as simple as a shift solenoid or transmission sensor or be the telltale sign of the beginning of an internal transmission part failure.