I know another overheating question but any input would b great

Ok so I've got a 98 4.0. 31's limited XJ. It's got a 180 tstat, new wp, new aluminum rad, new zj fan clutch, new heater core, new temp sensor, new flippin every thing. Swapped water pumps twice. Several diff thermostats. Two diff rads. Everything serviced, oil filters plugs. Runs great. All parts I got from napa. Several mixes of coolant. Now here is the issue. At cruising speed on the streets or freeway it's runs cool180-190 but when I'm crawling or sitting in traffic it goes up to 220-230 at which point it starts boiling over in to the overflow bottle. Should it boil over at such at low temp and why the 40 degree change in temp. just did the zj clutch and it is annoyingly loud but pulls a ton of air. I also did the electric fan mod. I can switch it on and it cools right down. The only issue I still have is the fan shroud is missing a piece about 5 inches long on the lower part where it sits on the rad, which I will be replacing this week. Any ideas what could be causing this and why would it boil over at about 225 degrees. Also I've never let it get too hot. I'm constanty watch the temp gauge and tired of it.

pressure test the radiator cap and make sure it'll hold at least 16lbs of pressure-- that's what keeps the coolant from boiling.

Ive got a handfull of caps ive tried but I haven't pressure tested any of them. But that makes me think maybe I've got a bad head gasket. That's about the last thing i can think of. Time to pressure test the whole system I guess. Is there a particular cylinder that is prone to issues?

Is there a particular cylinder that is prone to issues?

on a '98-- not really.

I'd check the cap first, and if it holds pressure, I'd check the rest, but I'd avoid checking the system at more than about 22lbs (you will likely find a weak spot that didn't exist before you pressurized it)

You said you did the E Fan mod, does that mean it no longer works automatically? When I'm sitting in traffic my fan will go on and off a lot. I think that's normal, is your E fan not coming on by itself? If not that may be your problem. I would test the cooling fan circuit to see if it's working properly. I know there are two relays and 2 fuses that power it (1 for A/C on and 1 for high coolant temp) some are under the hood and some are inside the jeep.

The e fan works as i it should. I can switch it on or the a/c will kick it on and around 220-225 I believe but but as the temp rises to the first tick mark past te mid it's already going into the overflow bottle. Should it be kicking on at a lower temp.

I think the FSM says it should come on at 218*. That is weird that it's still overheating though, especially with all the nice new stuff. Are any of those caps you have new, maybe a nice new one might be better? All I can think of is maybe they gave you the wrong water pump (spinning wrong way) or something more serious like a cracked head or something. Is the air path in front of the radiator clear, not blocked by a huge winch and a hundred lights? Maybe also try a cylinder compression test along with a radiator pressure test to see if your loosing anything either way. How's the oil and coolant look?

EDIT: E fan should come on at 223* and go off at 217* normally so that may be normal. The boiling over would be the primary issue then so I would look at the pressure situation then. If it's not holding pressure it will overheat earlier.

Nothing but a couple lights on the front blocking air flow. The coolant and Oil look good. The oil is normal looking(not a mocha color like when there is water in it and the coolant is a nice clean green color. I think I've tried 3 maybe four new rad caps. Oh and all the hoses are new and the heater core is new also. The lower has the spring it to keep it from collapsing. Think I'll take a couple caps tomorrow and have them tested also I'll pick up some of those coolant test strips that test for exhaust gasses in coolant. I did a full tune up a couple months ago, cap rotor, wires plugs and the plugs all looked good. Nice color and dry.

If it was a head gasket wouldn't it be over pressurizing at higher rpm's?

Pressure test results-
16lb cap, held between 15-16 psi for 15 min before I removed it from the tester
Engine while cold @ 16 psi, held for 20 min before even the slightest drop then removed tester
Cold Engine and started at 0 psi, outside temp around 70. Took about 5 min to reach 190 and 7psi-8psi at idle for 20 and of course this time it stayed at 190-200
The max psi I saw was 8-9 psi
So at this point I can say it is not a head gasket issue