99 Yukon sometimes doesn't start up right away

My Yukon, with 140,000 miles, will sometimes start/fire up right away but other times it sluggish to start and then when it finally does it will shake for a while. Also, sometimes when idling at a stop light it will shake. It will also shake sometimes when I get around 60-70 mph. The rpm's are fine.

I replaced the fuel pump last spring and had a tuneup last summer

Any ideas on what could be causing this? I've had my mechanic look at it and he's hooked up his handheld diagnostic tool to it and it never shows any codes

Thanks!

When was the fuel filter last changed?

And recheck fuel pressure, some pumps can fail prematurely.