1991 GT Running Poorly...Help

Hello All,
I have a 1991 GrandPrix GT 3.4l Dual Twin Cam, it runs okay when
its cold, as I drive more it starts to idle very poorly, rpms up and down,
and when I am shifting down its like its going to stall and sometimes does just die.
If/when it does stall it starts right up again but will pick its spots
to stall and run poorly.
I have replace an IMAP sensor and the Air INtake Controller, and fuel pump, these are items my mechanic felt could be the problem.
If anyone has a suggestion it would be appreciated.

Thanks, John

Have a dealership take a look at your crossover linkage. It is probably cracked and that would cause you the problems you are having. The cost is high for that replacement part and in the past it hasn't lasted very long. I think J & M has an aftermarket part a lot less expensive and it will last. Hope this helps you out.

Jason

I had a similar problem, and the dealership replaced the upper and lower intake gaskets. Apparently, they get brittle when they get old and it somehow affects the airflow depending on temperature.

I don't know what a crossover linkage is, though.