I have an 85 transam carburetted 305v8, & when driving home, as I arrived & put the selector in park, the engine felt like it was either damp or not firing on all 8 cyclinders. I have removed spark plugs, checked HT leads are making contact, distributor cap...but still it is running real bad. Any ideas what it could be ?

 

When you remove the distributor cap, check to see if the shaft in the distributor is sloppy, this is common.