I had a 2004 Pontiac Montana that had transmission woes several times. I chalk that up to the stupid Pressure Control Solenoid / computer control.
The 3400 V6 developed a head gasket leak and intake manifold leak. After repairing that a couple of the rocker mount bolts ripped the threads out of the aluminum heads. I heli-coiled the heads to repair it and debated heli-coiling them all. Someone I talked it over with told me to only do the ones that wouldn’t torque to spec. That was a mistake because after getting it back together and running it for awhile more stripped out. After heli-coiling them all I never had a problem with that again, but while bolting the intake manifold back down it stripped the threads out of the head so I had to heli-coil those.
The plastic coolant fittings that were used to connect to the heater core were prone to failure and vacuum connections around the throttle body were another horrible design.
The 3400 V6 developed a head gasket leak and intake manifold leak. After repairing that a couple of the rocker mount bolts ripped the threads out of the aluminum heads. I heli-coiled the heads to repair it and debated heli-coiling them all. Someone I talked it over with told me to only do the ones that wouldn’t torque to spec. That was a mistake because after getting it back together and running it for awhile more stripped out. After heli-coiling them all I never had a problem with that again, but while bolting the intake manifold back down it stripped the threads out of the head so I had to heli-coil those.
The plastic coolant fittings that were used to connect to the heater core were prone to failure and vacuum connections around the throttle body were another horrible design.