I just want to take a moment to thank all of you for all the helpful posts on different problems. Every time I have had a problem, I haven't needed to post becaue someone else already has and I found my answer. You folks are good!! All have been right so far.
My current problem is shuddering at low RPM, especially when gear shifts at around 40-50 mph. I suspected a plug/wire problem, but no, my handyman stepson said fluids (he'* just learning to fix cars). So, he checked 'em, tranny fluid low, put more in but checked the fluid level while car was in Park on a very slight incline. I thought you had to have it on a level surface and in neutral. At least we agreed that the engine had to be running. Anyway, still shuddering. Was this because of how the level was checked? Also, what are good spark plug/wire brands to get? What size socket do I use to remove the plugs or is it a special one I need to pick up. Mine is a 1993 Bonneville SE and the owners manual was lost eons ago so I don't hjave access to this very basic info. I love this car and would hate myself if I find out I ruined my baby. Thanks.

When was the transmission fluid and filter last replaced? If it has been a while, start with that. The transmission should be at operating temperature, engine running, in park (neutral will do, but is safer in park) on a level surface, when the fluid is checked.

Autolite, AC/Delco, NGK are good plugs, for a start. Autolite, AC/Delco, Belden premium for NAPA are good wires.

Edit - and welcome to our little corner of the internet.