My 95 Z28 with 171,000 is having trouble downshifting at 40-50 mph.Otherwise it runs fine. I had new plugs at 125,000. Where do I start? I'm thinking about wires?

 

no idea man.

 

It would be nice to know what transmission you have, and what you areexpecting in a downshift..

 

Forgot to say it was an automatic. Between this morning and tonight it started idiling rough and also doing the same shaking at a 20mph downshift. It feels like it is missing under load.Thanks for your interest and help.
Rich