GMC Repair: Car surges, vacuum leaks, pontiac firebird

Question
My wife has a 1995 Pontiac Firebird that she purchased new.  It has the 3.4 engine with an automatic transmission with overdrive.  She had been complaining of the transmission slipping for quite some time and I could never feel it.  I was finally able to feel what she was talking about and it feels more like a surge than the tranny slipping to me.  The Service engine light started coming on so I took the car to the dealership and they ran a diagnostic. It came back with a code 77 that indicated that the EGR valve was sticking.  I have replaced the EGR valve but the car still surges when trying to hold a steady highway speed and going up hill.  It also has some hesitation when accelerating.  I understand that pontiac's might not be your area of expertise but was hoping GM products might be similar.  Any help that you could give me would be greatly appreciated.
Thanks
Doug  

Answer
What was the LAST repair on the vehicle ?. ANY repair of any nature ?. In most cases problems that arise days, weeks or even months later can usually be traced back to the previous repair.

Usually the EGR has an EGR CONTROLLER of which is the electronic unit that sends a metered amount of engine vacuum to the EGR valve.

A diagnostics needs to be performed on the CONTROLLER.

If you have ANY vacuum leaks of any kind on the engine due to cracked, broken or disconnected vacuum lines you will get a surge problem.

Take the vacuum hose OFF of the EGR valve and plug the open end of the hose with a golf tee or a pencil and drive the vehicle for a few miles and see if your surge is gone.

Let me know. Don't worry if the CHECK ENGINE LIGHT illuminates, We just want to see IF the surge is gone.

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