1994 Mercury Tracer

I have this excellent little car which has not given me any headache on its 210K miles so far. In the last four mounths, however, I started to notice that the engine starts kind of trembling on 5th gear and loses its power as if sothing chokes it, if I keep pressing the gas pedal it will make it worst, but once I let it go or shift down to 4th gear it reasumes normally for a while and then comes back again. I was told this could be a ignition coil or an axle problem.

Many thanks for your help and advise.

Not axle problem. Could be a clogged catalytic converter. An ignition coil would not hurt. Has the plugs and wires been changed?

Many thanks for your response. plugs changed 2 yrs ago and wires about 4 yrs.