My 2003 Lesabre has rough idle and studder on hills. This is what I have done so far.
At first I got a SES, had code read at Autozone - Miss fire #5 cylinder.
So,
- Did wire and plug change - same issue, SES light now out
- Cleaned MAF, replace PCV and MAP sensor - same issue
- Cleaned fuel injectors and replaced fuel pressure regulator - same issue
- Replaced forward O2 sensor - same issue
- Pulled each ign. coil cleaned ICM post, checked Ohm at ICM plugs .5 and posts 5.5 on each (good) - same issue

I am out of ideas especially with no SES displaying. Seems to happen with engine hot and pulling a load up a hill but also rough idle.

Up next replace ICM, TPS, IAC

Are you loosing coolant? That engine is famous for ingesting coolant at the upper and lower intake manifolds. Cylinder 5 is right next to a coolant port as well.

I haven't noticed a loss of coolant

I would do a coolant pressure test and take a hard look at the lower intake gaskets.
You might also have a vacuum leak somewhere causing a lean missfire which also can be caused by the lower intake gaskets. They were a crappy plastic design from the factory. The gasket has since been updated with a aluminum gasket.

After I thought about it for a bit if the EGR valve is stuck open a little it will cause it to idle rough and miss up hills as well.

x2 egr is pretty common as are vacuum leaks not necessarily related to manifold gaskets.

X3 on EGR. But a minute coolant leak into a cylinder can still cause a misfire. Did you check your coolant reservoir?

he said there was no more codes

If I remember right, by 2003, wasn't the redesigned upper plenum, with a larger EGR hole used?

Plus, he says he is not losing coolant.....

Certainly sounds like a misfire.....he changed plugs and wires(OEM?), but did he check spark output for each coil terminal?

He should drive the vehicle on the highway, at 55 mph, up a slight grade....then, SLOWLY accelerate(to keep the TCC engaged).....if this can induce a misfire, then it'* generally secondary ignition......

He said he didn't NOTICE a loss of coolant, thus why I SPECIFIED to look again.

BTW Gus, did YOU get my PM?