The transmission does not shift past the second gear and at mere 80KM/hr 5000rpm noticed. Then engine overheating light comes on. Yesterday the coolant fluid hose from the top of the engine blew off loosing all the coolant. Quickly stopping and allowing the engine to cool with hood open saved it. It is not seized. However the 90 degree elbow feeding the coolant to the top of the engine will have to be replaced.
Me thinks your transmission is shot. Transmission overheated, cause the coolant to overheat and blew out your hose.
The transmission shift ing problem might be pretty easy for your shop to solve. Might just be a sensor problem. Suggest to get your shop to focus on solving the transmission shifting problem.
You need to find a good, well established transmission shop and have them check it out. That does not mean AAMCO, Cottmans, etc.
If the transmission has never been serviced then odds are it is damaged goods now. If the fluid is dark brown or black odds are it is fried.
Just an FYI. The fact your engine did not seize does NOT mean it is not damaged. Severe overheating can cause cylinder wall damage along with piston ring damage.
Excessive heat can cause rings to lose their temper and that means spring tension; not a frustrated emotional state.
It would be a good idea to keep a close eye on engine oil levels.
Most buicks aren’t designed for extended 5k rpm operation.