Transmission acting up at 45 to 60 mph!
 

Hi, we had our Pacifica Limited 07 (4.0l 6spd) for 2.5yrs now, after a 1000 mile trip going up and down hills the transmission started acting up as if it was going between two gears at 45 to 60mph.
The transmission has not been the smoothest thing since we had the car but the hard shift was at lower speed 2-3rd gear. Now this new problem does not seem related.
With everything I read on this forum it looks like the problem with these cars are the torque converter, the engine mounts and the transmission.
Since my car does not have warranty anymore, it would be important to have a proper diagnostic as All these parts are expensive and cant afford replace them all.

Any one experienced a similar problem? What was done to repair the problem and how much should I expect to pay?