Rough idle on start

Ever since the new engine swap, on startup after sitting for a while (overnight at least) the Jeep starts fine but the engine stumbles, seemingly missing on a cylinder or two. This lasts maybe 30 seconds and disappears if I drive off. Sounds like a leaky injector, but I pulled the injector rail, and on the advice of other posts about this turned the key to on for a few seconds and watched the injectors for any drips of fuel. Couldn't see any, so I reinstalled. The #1 injector does have an O-Ring that difffers from the rest, a little loser around the injector but it seemed to seal fine when I put the rail back in. '98 btw.



Other things I should be looking for?

Check the fuel pressure after turning it off and sitting overnight.

The symptoms are likely from a faulty check valve and/or a slow dribble on one or more injectors.

Where is the check valve on a '98? Can't find it in the parts manual.

NM, I see its built into the fuel pump assembly.