[stang65fst]

I was driving my truck last night and it has been running rough (possible injector, but I had parked it and haven't had time to get it to a shop) so I took off last night in it and as I was going down the road the speedo would jump so at 20mph it would fall to 10mph and then spike back to 20mph and it would do that at different points from 0-70mph.

Anyone have any insight on this for me?

 

[Pinesman]

vss? I think this makes the speedo jump and may cause your other problems. I'm sure somebody more knowledgeble will jump in.