I don't see why the gearing is being discussed, unless you think somebody put very small tyres on the car?
From the handbook, the following Maximum speeds in Km/Hr are given...
1st 43
2nd 74
3rd 113
4th 160
5th 161
Reverse 43
The catalytic converter can collapse and fail with old age, has this been changed or checked?
Otherwise if you are confidem=nt with all the wiring and sensors like the lambda probe, I suggest you take off the cylinder head and clean it up and reseat the valves, then adjust the shim clearances. I think a long life of slow city driving can make things a bit blocked inside....