Why does a 1990 Buick Reatta automatic transmission not shift into third gear?

A 1990 Buick Reatta not shifting into third gear could be due to several issues, including low Transmission Fluid levels, a faulty shift solenoid, or a malfunctioning governor. Additionally, problems with the transmission control module or internal transmission damage could also prevent proper shifting. It's advisable to check fluid levels and connections first, and if those are fine, a professional diagnostic may be necessary to identify and resolve the issue.