Engine shakes in idle (park, neutral, drive) and at speed. No real loss of power, and it does not seem to change with speed. Plugs and wires were changed by a mechanic about 6 months before this started. The truck has 240k miles on it, so I suspect it may be an engine or transmission mount, but before I start inspecting it (I have to put it in a location I cannot keep there for long) I want to run through all possibilities. Thank you.
Could still be an engine misfire or the mounts as you suggested. If it was a consistent misfire, it set a code and illuminate the check engine light on the dashboard. If there is a higher than normal idle along with it, don’t rule out a vacuum leak. Since it happens at idle in park that rules out quite a bit. I think you are on the right track.