First time ford

I know this general question has been addressed on hear a lot but I cannot find an exact fit. Ever since I bought my truck used it has had a miss, shudder or something like that around 45 to 50mph and it does not do it all the time. Lately it has been getting worse and today it finally got so bad that it will barely run. When I first checked, I had spark at all cops but then it would not start at all and I checked and there was no spark at the cops. Any ideas on what it is or what to check would be great.