[me and my metro]

What you describe is the standard failure for the Metro transmission. Be aware there are four different ratio transmissions for these cars. There are early and late cars, there are also three cylinder and four cylinder versions of both body styles. The four cylinder cars have higher gears and the poor late four cylinder cars have the lowest 4.4 final. There is a chart on here somewhere on the ratio to crown wheel gear count to determine final drive ratios. The finals are 9% different they range from 3.5, 3.8, 4.1 to 4.4 roughly.
Be aware that you may install a used transmission and have the same problem. These cars are getting pretty used up, they haven’t made them since 2001.